How can I see that N_q is odd if, and only if, q is of the form p^k with k a positive integer and p a prime congruent to 5 or 7 modulo 8?

Let q be an odd positive integer, and let Nq denote the number of integers a such that 0 < a < q/4 and gcd(a, q) = 1. How do I see that Nq is odd if and only if q is of the form pk with k a...

12 December 2015 2,733 4 View