%I #9 Mar 31 2024 15:07:36
%S 11,13,17,31,37,53,59,73,79,113,131,137,139,157,173,179,191,199,211,
%T 233,239,257,271,277,293,313,317,331,337,353,359,379,397,419,431,433,
%U 439,479,499,557,593,599,613,631,653,659,673,677,719,751,773,797,811,839,853,857
%N Primes for which -20 is a primitive root.
%H Vincenzo Librandi, <a href="/A105892/b105892.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Pri#primes_root">Index entries for primes by primitive root</a>
%t pr=-20; Select[Prime[Range[200]], MultiplicativeOrder[pr, # ] == #-1 &]
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Apr 24 2005