#elementary-number-theory
1 messages · Page 62 of 1
well a^b+1, looking at this form whats the first thing that comes to ur mind
fermat
thank you for the hint
can someone explain the Chinese Remainder theorem to me? it keeps coming up and I can’t make sense of the wikipedia article on it
hmm how much algebra do you know(ring theory etc)
if not we'll go for a more elementery aproach
I’m in linear algebra (matrix theory) now
hmm ok try reading this, its well written
you can inquire about anything that confuses ya
okay thanks
brb
I don’t understand this statement about extended euclidean algorithm
its essentially to find the inverses
an example probably will help
“It is wellknown that if gcd(a,b) = r then integers p and s exist where p(a) + s(b) = r”
(bezo'uts)
yep
but the eea seems to require a lot of iteration
its relatively efficient, but this is not really the important part. The important part is to get the theory that there are inverses and what follows
(if ur doing problems by hand usually finding inverses will be easy, and if not then computers already have eea coded)
wherever thers ^(-1)s or 1/something, it means modular inverse
so i’m confused as to what step 3 is saying
with respect to what
umm it says mod n_i
like you can’t say the modular inverse of x
you have to say the modular inverse of x to 26
i mean it literally says what mod tho
yep
I don’t get why it’s so complicated
like, intuitively it seems like it’s not that hard to find a number satisfying multiple modulos
well its not really easy to do so
like think about inverses, even those arent easy to find
the existence itself isnt hard to show with less tedium, but to actually compute it is annoying yeah
but like
if you were to say a number is 5 mod 12 and 9 mod 20
I can easily think to myself, well, the LCM of those is 60 so it’s X mod 60
and then I think, what numbers are 9 mod 20? well, 9, 29, and 49
well you dont need to check a lot of things, u only need to check a few here
and only one of those is 5 mod 12
I’m guessing that the second step is what makes it hard?
yeah like if u have 3 numbers its p easy to see it right
but if u have bigger numbers i think this is inefficient compared to the other algorithims
but which step is the hard part?
step 2
finding the list of things 9 mod 20 or figuring out which of those is 5 mod 12?
the latter
(also imagine having more mods to consider, that becomes more inefficient, like instead of 2 if you had 5)
I only care about 2 at the moment
Say you have a number
and you know it’s a mod c and b mod d
and c is larger
I’d think you could find y = d - c mod d if c mod d =/= 0 and 0 if c mod d = 0
hang on a sec let me
okay I think it’s like this
you have a number X
a = x mod c and b = x mod d
c > d
let y = d - (c mod d)
let z = (a-b) mod d
let n = (z/y) c + a
then n = x mod (LCM(c,d))
I don’t know how to prove it but I think that’s right
no need for c and d to be xp prime btw
oh, and if c mod d = 0 then the LCM is already c so it’s trivial
a^b + 1 is prime, then a even and b is power of two
Okay a has to be even, because otherwise (a^b + 1) would be even and therefore divisible by 2
why is it prime?
yeah thats one part
deekaan
the second part I can't figure out why
well a^b+1^b
think about factors
also notch im p sure this isjust what the wiki says for 2 primes
what wiki
the brilliant one i sent you
and wdym two primes?
where does it say that?
i mean i just glanced at it, but urs should be equivalent to the algo they have
for the case of two mods
otherwise its incorrect
the only algorithms I see there are iterative though and mine isn’t at all
The second part is because of factorization, if b is uneven then the expression (a^b + 1) = (a + 1)(***)
and if its not a factor of 2 then it can be turned into an uneven factor using prime factorization
is this right?
yep
okay wow thank you very much
Alright, I am stuck, i got this problem which I need to solve:
$\frac{x_1+x_2+...+x_n}{n}\geq(x_1x_2...x_n)^{1/n},~ \forall n=2^k,~ k\geq1,~ \text{and}~ x_1,x_2,...,x_n>0.$
Kaynex:
thank you
Yaya we just use $ surrounding here
aight, will keep in mind
I went through the whole method for induction problems
I started with assuming that it's true for a k, and went from there
however i couldnt do anything with the expression for only k, so I thought I'd work with k+1 instead
that didnt help either
so any advice or tip is appreciated, however no solutions please heh
I've managed to get this, dont know if it's useful tho
ok i think i got it
so uh what i did is rewrite the (x1.x2.x3..xN)^1/N where N=2^k as k products with two terms each
like (x1.x2)^1/2^k
now ${(x1.x2)}^{1/2^k}<=(x1.x2)^{0.5}<=0.5*(x1+x2)$
Lionel:
latex is aids but tolerate
no actually i skipped alot of steps
this is what i was trying to get at
you can use the same method for higherpowers
the steps will just be repeated
@queen locust
how do you find num of solutions to a polynomial congruence that could look like a quadratic poly with substituion?
i.e $x^{20}+30x^{10}+300=0 \pmod{249}$
Slate:
you could rewrite this to $z^2+30z+300=0\pmod{249}$ and then you would use lagranges numbers to find number of solutions to this
Slate:
but i dont think this is right because x^20 can have at most 20 solutions while ^2 will have at most 2
That's not true
The equation x² = 1 (mod 8) has 4 solutions
You need to be careful when working with composite modulus, so your first step should always be to use Chinese remainder theorem to split things apart into prime modulus
It doesn't matter x² - 1 = 0 (mod 8) has 4 roots
It's true if the modulus is prime
And that's why you want to use crt to work with prime mod instead
the odd number i wrote was supposed to be prime
as mod
i forgot to mention i have a prime modulus
and the 249 i typoed wasnt prime
Then the problem is that z will have two solutions
but x could have up to 20
But you have that x^10 = z
So there will be ten solutions (counting multiplicities) for x for each solution of z
but then you have to rule out the multiplicitites and to find the number of unique solutions you need to enumerate the solutions
you can use quadratic/5-th power residue things to say how many solutions you have
is it necessary to prove that eulers function is strictly nondecreasing
I don't think so
let c = d+1, for example. then y = d-1, z = a-b so n = (a-b)(d+1)/(d-1) + a which is not necessarily an integer
z =/= (a-b) though
it equals (a-b) mod d
let’s try a = 2 c = 20 b = 3 d = 19
y = 19-(20mod19) = 18
z = (2-3) mod 19 = 18
18 * 20/18 + 2 = 22 which is correct
@wild zinc
a-b is kinda irrelevant because it's arbitrary
you would have to have (d+1)/(d-1) an integer
your claim is that this holds for all a,b?
for all a,b and c,d yes, assuming there is a solution
so it wouldn’t hold for 3 mod 18 and 2 mod 16 for example
but if there is a solution with a,b I think this finds it. I’m not sure why though.
what about a = 1, b = 0, c = 17, d = 18
y = 17-(18mod17) = 16
z = (0-1)mod17 = 16
16/16 * 18 + 0 = 18
a=1,b=0 shouldn't work tho
oh, a = 1, b = 0, c = 18, d = 17?
maybe
yeah, I forgot which way round I did the +1
we get 9/8 + 1
I think if you let the division be modular inverse then it holds but
this has the same problem of requiring modular inverse calculation
hang on
is there an easy way to manually check numbers
like somewhere I can put these equations and change numbers on the fly
learn some basic python and program it
easily brute force check for counter examples
what I don’t know how to do is test only valid a,b pairs
I wouldn’t want it stopping on 0 mod 2 and 1 mod 4 for example
what is the criteria for being a valid pair
I think that A and B have to be equivalent modulo (GCD(c,d))?
then only test ones that satisfy that
is that correct condition?
I have no clue, why are you asking me
I didn't read the problem, it didn't interest me
you were responding to my questions about the problem
but I'm just offering to help you set up your program
ah
but you don't know what the criteria is to check so I can't help, good luck
I assume that’s it
sounds sketchy
just
you only want to check the true cases to know what's true...?
the criteria I want is for one number to be a mod c and b mod d
and I’m testing how to find that number
and I only want to check cases where that number exists
I see
which python version do I get? python 3 or python 2?
what’s that
and then I think it will take care of getting the stuff you need from addons in it
it's an IDE
basically like, spell check for code
and runs code too
like, very roughly speaking lol
might be better to find a kind of tutorial or something to learn some from since you might have to learn a few things before you can write a few for loops to get what you want but it shouldn't be too far off
no I have basic python experience
It’ll just take me a bit to refresh and check how to use mod operator and that sort of thing
if I have p = 3 mod 4 and a =/= 0 mod p, how would I go about showing either -a or a == b^2 mod p where b is some integer?
this would follow from the fact that -1 isn't a square mod p
Could you please explain more?
visual studio code?
make a new thing like test.py
it might recognize the file name and ask if you wanna add stuff
it'll give you a run button at the top right once you install what it prompts
possible
oh wait do I need to name it .py?
yes
lol yeah that would do it
@sacred junco there's a fact that the product of two things that aren't squares mod p is a square mod p
So like if a and b are both not squares mod p, then ab has to be a square mod p
So if -1 isn't a square mod p and a isn't either, then -a has to be a square mod p
can you help me?
I probably just messed something up but my code isn’t working and I’m not sure why
copy paste it
hang on let me open discord on my computer
import math
for c in (3,100):
for d in (2,c-1):
lcm = (c*d/math.gcd(c,d))
for x in (0,lcm-1):
a = math.fmod(x,c)
b = math.fmod(x,d)
y = d - math.fmod(c,d)
z = math.fmod((a-b),d)
if z == 0:
n = 0
elif z > y:
n = (z/y)*c + a
else:
n = (y/z)*c + a
if n != math.fmod(x,lcm):
print (a,b,c,d,x)
print ("done")
um, the * symbol for multiplication is making things italic
how do I fix that
put three ` before and after
import math
for c in (3,100):
for d in (2,c-1):
lcm = (c * d/math.gcd(c,d))
for x in (0,lcm-1):
a = math.fmod(x,c)
b = math.fmod(x,d)
y = d - math.fmod(c,d)
z = math.fmod((a-b),d)
if z == 0:
n = 0
elif z > y:
n = (z/y) * c + a
else:
n = (y/z) * c + a
if n != math.fmod(x,lcm):
print (a,b,c,d,x)
print ("done")
for i in range(1,100):
print(i)
oh did I forget the word range? is that all?
I didn't look at your code I was just saying put three ` before and after to format your code
and gave an example
if your code is broken test individual pieces in smaller chunks rather than doing it all in one huge thing
Solved it nvm
new question
apparently python interprets “fmod(-2,5)” to be -2
when it should be 3
how do I fix that
k, I just add the 5 to the -2 until it’s above 0
i know that K is a k vector space but i'm not sure how to show K is finite dimensional
i was thinking of finding a basis, but i have no idea how
i can also try to argue that field containing finite dimensional fields are also finite dimensional, poor wording ik
@winter bear help me papa
hmm gimme a sec i think i have a proof for this written somewhere

i mean, the idea is to induct
start of by removing one root, and then extend this new field by removing another
i'll give induction a shot
okay i'm still not sure how
i want to prove that $[k(\alpha_1):k]$ is finite right, and then keep adding on more $\alpha_i$ until it hit $\alpha_n$
kinda
Publius:
i mean basically
lemme refine this for you a bit by giving you an inductive hypothesis
but i need that as a base case tho
unless you're talking about a different induction
$P(n)$: for each poly in any field of degree $n$, theres a splitting field thats a finite degree extension of this field
JohnDoeSmith:
i mean this is kinda equivalent to your idea of "keep adding a_i"
tru
i see
let me give that a shot
i'm still not sure where to complete the hypothesis

the first line assumed f is degree 1
and green marks the degree of f
i mean the idea is basically right? try to refine it, for example f(x)=x-a splits in k, no need to say k(a_1)
also i think it would be nicer if you directly use prop 7.2.1
but yeah idea is correct, you reduce the degree by finding a field for one of its roots, and then by induction that splits in a finite extension field
i sort of did by assuming those $K_{\alpha_i}$ exists?
Publius:
but i just don't see where to go with this induction
oh right ok so
yeah
but ill say, its nicer to consider just one root
rather than all that i roots
basically
but induction tells me to assume it for arbitrary number of roots no..?
Just remember that if K is contained in L, [K(a):K]>=[L(a):L]
i mean yeah idea still works i wont complain about the asthetics ig
hmm
You probably also want to verify that adjoining elements maintains field structure
Which can be done inductively as well
okay i'm actually still stuck
what am i doing wrong 
am i suppose to say deg f = i?
my small brain just can't make sense of this
ok so lets say f has deg i+1 right
mhm
by prop 7.2.1 we can find a finite extension of this such that theres a root, i.e f(a)=0 right
yes
g splits since it is degree i
mhm, specifically splits in a finite extension
right
hmm, but what field does f splits then?
is that field K + [field that g splits]
ok so we extended $k$ to lets say $K_a$, and then we extended $K_a$ to lets say $K_a'$, i.e where $g$ splits
JohnDoeSmith:
so where does f split here
the reason why the second extension from K_a to K'_a is finite is because degree of g is i?
yeah, by inductive hypothesis we can make a finite extension of g since its deg i
np son
Is it bad that I didn't use the second property (ii) in the proof?
wait, i need it for proving the first direction nvm
so by euler's theorem, f = phi(n)
i also note that i can factor out x-1 in x^n - 1
but other than that, i'm pretty clueless
hint pls
so first its not phi(n)
the order itself can be smaller than phi(n)
for example, 2^3=1 (7)
and heres your hint
$n|q^f-1$ which is also the order of the multiplicative group
JohnDoeSmith:
@alpine jasper
hmm i dont see how ker dividing |E^x| told u n|q^f-1
if G a group and H a subgroup, |H| | |G|? is that the lagrange theorem or somethin
kernel has size n since we're basically working with nth root of unity?
i'm not entirely sure
uh huh
you couldnt find a splitting field in the first place if q|n btw
is where this would fall apart
for the (q,n)=1 condition
is unsolvable if (n, q) != 1?
also that
hmm my smol brain don't immediately see why
ill let u work it out
but as to the bigger problem
you have shown if $x^n-1$ splits in extension of degree $f$, then $n|q^f-1$ right.
JohnDoeSmith:
but unfortunately this doesnt tell you wether f is minal and when n is minal
so what do you think you should do
oof i mispelled minimal twice the same way
hmm yeh good point
think about it for a bit, its p similar to this to show the other part
np
i think this shows that gcd must be 1 otherwise the eq. is unsolvable as expected
but i'm stuck on how to argue the minimality of f
yeah, btw what u did is basically euclids algorithim for gcd
yeah i've noticed
that gcd=1 implies solvability?
i see
i'll give it a shot
ty

idk how
i also don't understand why splits iff n|q^f-1 implies f is minimal
well remember when u solved x^n=1 in fields right
uh huh
how many solutions and what was the criterion for solving this
n solutions, (n, q) = 1
and what else
umm lemme phrase it like this
how many sols does $x^n=1$ have in $\mathbb{F}_{p^k}$
JohnDoeSmith:
prolly look back in IR if you dont remember
hmm
wait (n,q) is tru nvm that
either 1 or n?
yeah, depending on what
since either just trivial soln or a non trivial soln which generates the rest
umm
n | p^k - 1
yeah, so do you see how this works then
ok
so if n|q^f-1, then x^n = 1 have n solutions in F_(p^f), so it splits in E?
F_(q^f) but yeah
am i suppose to write F_(q^k) instead?
umm not really. theres only one field of each order so as long as its clear what the order is its fine
hmm alright
i still don't understand why splits iff n|q^f-1 implies f is minimal tho

well take the smallest f such that n|q^f-1
what happens if there is some f'<f
such that extension of that degree splits the poly
oh right that makes no sense i just realize
i should think about why that extension dne
another way to look at this that extension degrees where this split is one-to-one corrospendence with f such that n|q^f-1
if that helps
thats ok
umm so
$f$ deg extension where $x^n-1$ splits $\iff$$n|q^f-1$. Take the smallest $f$ such that $n|q^f-1$, if there is a smaller degree extension $f'<f$ where $x^n-1$ splits, then we know $n|q^{f'}-1$, but this contradicts minimiality of $f$.
JohnDoeSmith:
well it was kind of a contradiction right
Take the smallest f such that n | q^f - 1
this is the important bit right
Take the smallest f such that n | q^f - 1
smaller extension that splits
implies
f is not the smallest
yeh.?
yep
yeah sure
uhh, so the idea is to reduce the degree that q is raised to all the way to 1
idk if that's a contradiction
probably pure garbage
well so one thing is that u arent garunteed to get 1
just gcd(f,s)
in exponent
(think about why)
and hmm i mean this isnt a contradiction
you'd have to use the corrospondence we used above
i think
yeah
i don't see how that works too
but i'm still not sure why the lowest is (f, s)
hmm do you see it cannot be any lower than (f,s)
ok so the exponent will end up as a combination of f and s right
and gcd divides both
oh.
to show its exactly gcd is a bit more slick
$q^f=1 (n)$, $q^s=1(n)$ then $q^{(f,s)}=1(n)$
JohnDoeSmith:
ill give u a hint if u wanna prove this
(btw it can be lower than (f,s), but u wont get that number by just this info, is what i meant)
i mean its a one liner
i feel like i just have to write out the defn
np
hello
i'm once again asking for your nt support
is this the set i'm considering?\
${x\in\mathbb Z[i]\mid x\equiv p(p)}$
Publius:
doesn't make much sense to me
this is the same as\
${x\in\mathbb Z[i]\mid p\text{ divides } x}$
Publius:
or is the set something else..?
i suppose that set would make sense
it has
p + pi
2p + pi
...
p^2 + pi = 0 + pi
and for each kp + pi, i can "branch out" the imaginary component so like
kp + pi, kp + 2pi, ... kp + p^2 i = kp
for p^2 elements in total
that seems too easy or am i missing something again
asking you to look at z[i]/(p) basically
this is a quotient ring right
yes
ok i should try to formally write down what this means my algebra sucks
$\mathbb Z[i]/(p)={a+bi+x\mid x\in(p)}$
Publius:
yeah
i'm not sure how to like, count it tho..
it looks like i can make the real part running from 1 to p
but do i have any control over b?
i'm being dumb again probably
i'd say b = d(p) and a = c(p)
actually
.. yeah?
{a + bi + x} = {c + di + x}
by this do you mean
${a+bi+x\mid x\in(p)}={c+di+x\mid x\in(p)}$
yes
Publius:
so ok, only b = d(p) is needed
are you sure? so {1 + x} and {2 + x} are the same set?
Sorry, I'm just writing the shorthand
I mean {1 + x | x \in (p)}
but remember that (p) is an ideal in Z[i]
so it has elements like pi
er p * i
oh wat
i thought its just 1, 2, ..., p-1
let me think about it
ok i don't understand why it'll have stuff like pi
(p) is the ideal generated by p
ok gud let's more forward
let me think about it for a sec
${1+x\mid x\in(p)}={1+p(a+bi)\mid a+bi\in\mathbb Z[i]}={(pa+1)+(pbi)\mid a,b\in\mathbb Z}$
Publius:
are you sure? so {1 + x} and {2 + x} are the same set?
so no afterall, if {a + bi + x} = {c + di + x}, then b = d(p) and a = c(p)
that is some gud shit
idk if this notation makes sense
to show that Z[i]/(p) is a field, should i try to show (p) is a maximal ideal or working with the RHS directly?
the former's easier
actually, why was the fact that p=3(4) never used? @light flicker
q is an element of Z[i]
so its not immediately true that since q |p that q = 1
here is where you use the fact that p = 3(4)
if p = 1 (4), for example if you take p = 5, then its not true since 5 = (2 - i)(2 + i)
welp
i tried computing the sum separately but no luck with the first one, and this is what i have so far for the second one
have you seen the proof of the euler product for the zeta function
this right, yes
but the form is not exactly right, for example, LHS has the base as n, but what i had above has it as p
i looked at it for a while and don't know how to apply it
It's the same idea
Look at the proof for the euler product for the zeta function
and adapt it
hmm alright
so i looked at the proof
and the idea is that i multiply and remove stuff with factors systematically
sort of like treating monic poly as numbers, and monic irred poly as primes
but i'm stuggling to formualize and figure out what to multiple and subtract
bascially i don't see what's the analogous equivalent thing to 1/2^s
Leonhard Euler proved the Euler product formula for the Riemann zeta function in his thesis Variae observationes circa series infinitas (Various Observations about Infinite Series), published by St Petersburg Academy in 1737.
$\frac{1}{1 - p^{-s}} = 1 + \frac{1}{p^{-s}} + \frac{1}{p^{-2s}} + \cdots$
Zopherus:
yeah, you should think of this fact as coming from the fundamental theorem of arithmetic
Basically if you take some number like 12
12 = 2^2 * 3
so to get 12, you'll multiply $\frac{1}{2^{-2s}} \cdot \frac{1}{3^{-s}} = \frac{1}{12^{-s}}$
Zopherus:
ok i'll think about that
It's kind of the intuitive idea why it works
So like the product is
$\left( 1 + \frac{1}{2^{-s}} + \frac{1}{2^{-2s}} + \cdots \right) \left( 1 + \frac{1}{3^{-s}} + \frac{1}{3^{-2s}} + \cdots \right) \left( 1 + \frac{1}{5^{-s}} + \frac{1}{5^{-2s}} + \cdots \right) \cdots$
Zopherus:
ok gimme some time to digest that
This is just rewriting the product
uh yeah, but i don't know how to adapt this
So the idea is that every positive integer can be uniquely written as the product of power of primes
Similarly, every monic polynomial can be unique written as the product of powers of irreducible monic polynomials
god damn
i just don't see what to do really
i'm suppose to multiply this by something in terms of monic irreducible poly right
call this original sum S, then suppose after i multiply, i get AS, then i do S - AS, which equals to S - some stuff that are not irredicuble
that probably made no sense
Idk, again
$\left(1 - \frac{1}{(Nf)^s} \right)^{-1} = \frac{1}{1 - (Nf)^{-s}} = \left(1 + \frac{1}{(Nf)^{-s}} + \frac{1}{(Nf)^{-2s}} + \cdots \right)$
Zopherus:
idk, if you want to do it the way that wikipedia does it
Then yeah, take some irreducible monic polynomial g
And if you do what they do
you'll remove all the terms in the sum that were divisible by g
idk where that second equality came from really
and yes i've been trying to do it analogous to the one from wiki with 0 progress
let me think about this more ig
the second equality is just geometric series
oh
i just don't think i can do it the way wiki did it
because the numerators
if i multiply everything by like, p/p^(2s) then do the same thing
the terms wouldn't like, line up
where are those p's on top even coming on top
i count by degree of f
but suppose degree f = 7, then i have x^7 + ax^6 + bx^5 + ...
oh wait did i counted it wrong
there are p^6 choices of degree 7 monic poly
and I'm not sure writing it like this will help you
$\zeta_R(s) = \sum_{f \in R, f \text{ monic}} \frac{1}{(Nf)^s}$
Zopherus:
then take some irreducible monic polynomial g
you have that $\frac{1}{(Ng)^s} \zeta_R(s) = \sum_{f \in R, f \text{ monic}} \frac{1}{(Nfg)^s}$
Since $(Nf)^s (Ng)^s = (Nfg)^s $

ok let me see if i can continue
ok i think i can finish it
just to make sure, 1 is not a monic irreducible polynomial by definition right? since it can't be factored into two non-constant poly
i see
This is by definition
thanks for your immense amount of patience my dude
You're lucky I've been grading and have nothing better to do
lmao
i'm stuck once again 
i completed 2 successfully but 3 is giving me a hard time
@light flicker
yeah im online now
Me too
@alpine jasper
oof
do you want me to repost the problem again
yeah
Did you figure it out
no i did not
wait ill let tree3 help u out here, cause i kinda have some hw to do
ok nice
N(n) is the number of monic irreducible polynomial in Z/pZ[x] where p is a prime
log(1-x) taylor series
You want to compare coefficients: the 1/p^(ks) coefficients should match up for each k.
let me try again i guess, i'm less tired than yesterday
mostly stuff written in blue
Yeah
Start by finding the 1/p^(ns) coefficients of both sides
Do LHS and RHS individually
gimme a moment i'll report back
so this is precisely where i'm stuck
i don't know how to deal with 1 sum on the LHS and 2 sum on the RHS
i tried to write it in form of\
$\sum_{\beta\geq1}\sum_{n\geq1}(\textit{stuff})$
Publius:
We want to find the coefficient of 1/p^(ns)
Which acts like an x^n coefficient for x=p^s
In -log(1-p^(1-s)), we get (p^(1-s))^n/n
=p^n/n(p^(-ns))
So the coefficient is p^n/n
let me digest that
gimme a moment
In $-\log(1-p^{1-s})$, we get $(p^{1-s})^{n/n}=\frac{p^n}{n(p^{-ns})}$
Publius:
In $-\log(1-p^{1-s})$, we get $\frac{(p^{1-s})^n}{n}=\frac{p^n}{n}(p^{-ns})$
tree3:
This is just from the Taylor series expansion
Um no because the stuff circled in purple can’t have an s in it
idk how to manipulate the RHS really :/
i also dont get the idea of matching terms, since i can have two different series summing to the same thing but the nth term need not be the same right?
On the RHS, we have terms in the form $-N(k)\log(1-p^{-ks})$, which when expanded give terms in the form $\frac{N(k)p^{-krs}}{r}}$. We just need to identify which of these terms correspond to $p^{-ns}$. This occurs if and only if $kr=n$, so to account for all possibilities, we just select $k$ to be any divisor of $n$ and $r$ to be $\frac{n}{k}$. This gives terms of the form $\frac{N(k)p^{-ns}}{\frac{n}{k}}=\frac{kN(k)p^{-ns}}{n}$, where $k$ ranges over the divisors of $n$. Summing these and comparing coefficients gives the result.
tree3:
Compile Error! Click the
reaction for details. (You may edit your message)
i don't think i'm getting the idea here
let me reread what you said above
so like this...?
i'm a big dumb
bc i'm only looking for coefficient of p^(-ns)
It should still be a double sum
i don't know what i'm summing over when i write kr=n
Divisors of n
i know that, i mean like, where i should put my second sum
There you go
so removing the 1/n term gives us the result
Yes
i don't fully understand how you turn the sum into that form, let me think about it more
thanks btw
The idea is that you want to find all terms corresponding to p^(-ns), so you set kr=n and solve for r in terms of k.
The new constraint is just k|n because k can be any divisor of n
Np
did i miss smth obv, why is the second equality true
Let p be an odd prime. Use Theorem 7.5 to prove that there is exactly one positive primitive
Pythagorean triple (x, y, z) with y = p, and find formulas for x and z in terms of p.
Theorem 7.5.
If (x;y;z) is a primitive Pythagorean triple, where x is even and x, y, and z are positive, then x= 2st; y=s2-t2; and z=s2+t2; for some relatively prime positive integers s and t. Conversely, if s and t are relatively prime, s > t >0, and s or t is even, then (2st; s2-t2; s2+t2) is a primitive Pythagorean triple.
I'm having some difficulty with how to go about this proof. I set y=p=s^2-t^2 but I see no way to write x and z in terms of just p.
Think about factoring s² - t²
Right, so p = (s-t)(s+t). Ohhhh -- but p is prime! So s-t = 1.
I did that earlier and i don't know how i missed that lol
Thank you! I got it now
let a be in N and p be a primefactor of n = (2a)^2 + 1
show p is congruent 1 modulo 4
I can eliminate 2 because (2a)^2 + 1 is uneven so 2 can't be a prime factor
but don't get much farther than that
@obtuse mason p dividing (2a)^2 + 1 means that (2a)^2 + 1 is 0 mod p
Then think about quadratic residue things
i dont really get where this um +uv= g comes from?
for this to be true, u and v would have to be non-integer?
because g is smaller than both u and v
oh are they using bezouts identity?
if so thats strange since bezouts hasnt been covered in the book yet
but thatd make the most sense yea
,calc xgcd(13,17)
Result:
[1, 4, -3]
,calc 413-173
Result:
1
Determine all positive integers $n$ such that $n^2$ divides $2^n+1$.
Plum:
consider the ||2 smallest prime factors of n||
hmm
That's an imo p3 lel
really?
Yes
yeah lol
its part of the amsp N2 pset bruh
can u give me another hint lol
umm ok start by considering smallest possible prime factor p of n
what can you deduce about p from this
Are you doing awesome math?
no the deadline passed but im trying some sample problems for fun
hm yeah im not sure
ok try arguing on order
so first definations
o lord
JohnDoeSmith:
wait (n/d) is the legendre symbol right?
oh no its just division lol
oh 🤦♂️
oh its associative commutative since ${ d | d\text{ divides }n}$ is the same as ${n/d | d\text{ divides }n}$
commutative* but yes
Plum:
The sol to n^2|2^n+1 is very short tbh
For associativity, think about convolution as sum ab=n f(a)g(b)
yeah^
||Clearly n=1 works. Suppose n>1 and let p be the least prime factor of n. Then p|2^n+1 and so p|2^(2n)-1. Therefore p|2^(gcd(2n),p-1))-1. p-1 must be relatively prime to n since it is less than each prime factor of n, so p|2^2-1=3. Hence n=3k. If k=1, then n=3 works. Now suppose k>1 and let q be the least prime factor of k. We have q|2^(3k)+1 and so q|2^6-1 for similar reasons. 2^a+1 is never divisible by 7, so q=3 again. However, since n is odd, 1+v_3(n)=v_3(2^n+1)>=2v_3(n), contradiction for v_3(n)>1.||
progress plum?
i think i have an idea
John was anything different in your sol
i think it was p much exactly the same, with minor divergences in the end
Forgot to say n is odd before lte oops
right my order of logic was a bit different then urs, but ultimately same thing ||i said power of 3 must be 1 before doing the 2nd smallest prime factor||
yeah my sol was the same as yours john iirc
I like getting contradictions lol
$f * (gh) = \sum_{ab = n} f(a)(gh)(b) = \sum_{ab=n} f(a) \sum_{cd=b} g(c)h(d) = \sum_{acd = n} f(a) g(c) h(d) = \sum_{ed = n} \sum_{ac = e} (fg)(e) h(d) = (fg)*h$
Tree is anti constructivist
Plum:
hold on i need to work on my hw but ill brb
Personally I prefer intuitionist proofs
By this I do not mean following intuitionist logic, but rather by saying "intuitively it seems true, qed"
alright we'll continue it after u return
Anyone have any problems
Yeah
What's 2+2
show spectrum of a ring is disconnected iff it contains a non-trivial idempotent
a) Find a nice way of writing 1 + 2x + ... + (n+1)x^n
b) Find a nice way of writing 1 + 3x + ... + T_(n+1)x^n
c) Find a nice way of writing 1 + (T^k)_2 + ... + (T^k)_(n+1)x^n
Where (T^k)_n is the n-th k-th order triangular number (the sum of the 1st n (k-1)th order triangular numbers)
(for example (T^2)_3 = T_1 + T_2 + T_3 = 1 + 1 + 2 + 1 + 2 + 3
By Hockey stick this reduces to 1/k! times some kth derivative
Is that considered “nice”
Hint: (this idea applies to all of them so be careful before deciding to read) ||let's look at a: denote the sum by S, S - Sx = -(n+1)x^(n+1) + x^n + ... + x + 1 = (n+1)x^(n+1) + (x^(n+1) - 1)/(x-1) and so forth||
Not sure what you mean tree
How is this “nice”
Just use finite differences for all of them
Don't know that
$$f(x)=\dfrac{1}{1-x} = \sum x^n$$ $$f^{(k)}(x) = \sum n(n-1)\dots (n-k+1) x^{n-k}$$ $$\dfrac{x^k}{k!} f^{(k)}(x) = \sum \binom{n}{k} x^n$$
Can you illustrate it
JohnDoeSmith:
im procrastinating xdd
oh oof
i think ill be finished at around 9 est if ur available then
T^k(n)=(n+k+1)C(k+1)
1/(k+1)!(d^(k+1)/dx^(k+1)((x^(n+k+1)-1)/(x-1)))
Now find all integral solutions to $n^420 - 1 | 420^n - 1$
Archsys:
My formula’s fairly succinct and leads to a closed form with number of terms independent of n by product rule expansion.
Is there a way for me to prove that if A and B are coprime, then there is a k in 0 to (B-1) such that kA = X mod B for any arbitrary X in 0, B-1?
do you know how to prove that the multiplicative inverse to A exists given (A,B)=1?
um
I’m not sure off the top of my head from an analytical level, but I can easily take your word for it
I can take that as a granted in what I need this for
Actually, is the thing I said I needed to prove enough of an established fact that I can use it in a proof of something else without having to prove it first?
Yes
But it really depends on what you are doing
If you're taking a number theory course, then your professor probably wants you to prove it
But if you're talking to people who know even a little number theory, then they know this fact
No, not a course
i mean ig proving this needs ||bezouts|| and the only proofs i know for that use WOP
Or || use Euclidean algorithm and argue backward ||
Okay second year ion
question*
if you have a prime A, and the next prime is B, is B guaranteed to be less than 2A? I’m pretty sure it is
but I don’t know for sure if it’s been proven
yes, its proven theres always a prime between p and 2p
It's called Bertrand's Postulate
its very high powered though, compared to what you are doing
I don’t think so
it’s more of a case of I cba to try proving those right now as I don’t want to get distracted from what I’m doing overall and lose my train of thought
BTW an elementary proof that multiplicative inverses exist can be done by ||showing that no two elements in {0, a, 2a, ... , (b-1)a} give the same residue mod b||
“I don’t think so” was bad phrasing and arrogant, sorry
it was more “I’m not sure”
oh thats smart gonzo
Gonzo, showing that no two elements have the same residue mod B is what I wanted to know if it was proven lol
Yeah, but formulating it like that is like half the solution
think about what if ax=ay mod b
Quick question.
I'm not sure I understand why, about 2/3 of the way down, each of a,b,c must be even.
Why couldn't, say, a be even and b,c be odd?
...is it because then you'd end up with a number congruent to 2 mod 4?
Yes

lmao
did i do smthn
What
so
I don’t want to sound stupid or like a crank here
I have in front of me what I believe to be a proof of the twin prime conjecture. I am also fairly certain that such a proof must be wrong because of how long people looked for one and didn’t find one, but I personally can not find any errors in it. Where can I put it to have someone look over it and see if/where there are error?
right here
like just type it out in the channel?
it’s a couple pages long in my word doc, is that okay?
Link it or upload
Um okay let me open discord on my computer
I'm sorry it isn't written formally I don't know how to do that
should probably remove your name from the doucment
I don't see how your earlier analysis, which seems correct to me, applies to the situation with Q, C and R
Earlier, when you were assuming you had a pair of twin primes, there was exactly one number N inbetween the twin primes
but here, there is no single number between Q and R, so you can't really apply your earlier analysis
The earlier analysis describes the property a number must have, the Q/C/R bit is about proving a number with those properties exists
Q and R aren't twin primes, they're the primes that are the equivalent of A and B in the earlier analysis
Then, I guess I'm confused what the "list of last digits" is
like
the last digits of what number
earlier, it was the possible last digits of N, but now there's no N
well there is an N
what you're doing is you're saying "If an N exists, it must have these properties; and if these properties are satisfied on a number then that number is an N"
and so the list for Q is saying "If an N exists, it must have one of these last digits when written in base C"
and obviously you can't immediately say "if these properties are satisfied on a number then that number is N" because the N could be 1 mod a prime above Q but below sqrt(N), which is what the section about G and F is dedicated to showing that a number has to exist without that problem
the list of last digits is basically saying "N = Y mod C" and the list is all possible values of Y
I'm just using the last digits phrasing because it's more intuitive to my brain so by using this phrasing I could avoid confusing myself when writing it up
what may help you is G is the equivalent of N
Okay, I'm also confused because, you're not assuming such a G exists, you're trying to show that such a G exists right
right
Then how can you let F be the largest prime below G - 1, if you don't know if G exists yet?






