Number theory

[waxen loom]

do you mean:
Let a and n be integers where n > 2. Prove that if a^n - 1 is prime, then a = 1 and n is prime.

and replace 2 with n in a^2 - 1

might as well replace it with
Let a and n be integers > 2. Prove that if a^n - 1 is prime, then a = 2 and n is prime.

for that, use that x^n - 1 = (x - 1)(1 + x + x^2 + ... + x^(n-1)) for the first statement
then use fermat's little theorem for the second statement