Quadratic nonresidues modulo a Fermat prime
= Quadratic nonresidues modulo a Fermat prime
{c}
For a Fermat prime $p=2^{2^k}+1$, the multiplicative group modulo $p$ has order $2^{2^k}$. Its $\varphi(p-1)=(p-1)/2$ primitive roots are all quadratic nonresidues; since there are also $(p-1)/2$ nonresidues, the two sets coincide.