Re: cyclicity theorem correction
> CORRECTED THEOREM--Richard Brent pointed out this theorem was already shown by Gauss, and
> is that the residues relatively prime to modulus M
> form a cyclic multiplicative group if and only if
> M = 2*p^k or M=p^k or M=2 or M=4,
> with k>=1 and p = odd prime.
it is in D.Shanks: Solved & Unsolved problems, theorem 42 on page 92.