%I #14 Mar 31 2014 04:08:22

%S 2,19,23,29,31,53,71,97,103,107,113,137,139,149,157,179,181,191,197,

%T 223,233,239,263,271,281,307,313,317,347,359,389,397,401,409,431,443,

%U 449,491,523,557,569,577,607,619,643,653,659,683,701,727,733,743,769,787,809,811

%N Primes with primitive root 21.

%H Vincenzo Librandi, <a href="/A019348/b019348.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 _David W. Wilson_