%I #9 Mar 31 2024 15:07:41
%S 2,29,47,53,59,67,83,97,113,127,131,137,149,151,157,167,181,197,227,
%T 233,251,281,311,313,317,331,379,383,389,397,401,409,419,449,467,479,
%U 487,499,503,557,563,569,571,577,587,647,653,701,719,733,739,751,769,809,821,823
%N Primes for which -21 is a primitive root.
%H Vincenzo Librandi, <a href="/A105893/b105893.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=-21; Select[Prime[Range[200]], MultiplicativeOrder[pr, # ] == #-1 &]
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Apr 24 2005