A much smaller simpler example would have been useful for us mere mortals. Ok 6 is not a prime. 5=b is not a multiple of 6 5^(6-1) = 3125 mod 6 = 5 which is

A much smaller simpler example would have been useful for us mere mortals. Ok 6 is not a prime. 5=b is not a multiple of 6 5^(6-1) = 3125 mod 6 = 5 which is not 1. Therefore 6 cannot be prime.