Primes

• Feb 12th 2009, 10:16 AM
wrighchr
Primes
Prove that if a is grater than or equal to 2, n is grater than or equal to 2, and (a^n) -1 is prime, then a = 2 and n is a prime.
• Feb 12th 2009, 09:59 PM
ThePerfectHacker
Quote:

Originally Posted by wrighchr
Prove that if a is grater than or equal to 2, n is grater than or equal to 2, and (a^n) -1 is prime, then a = 2 and n is a prime.

Hint: $x^n - 1 = (x-1)(x^{n-1}+...+x+1)$.