This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A240108 #7 Jul 17 2025 12:05:26
%S A240108 3,9,13,17,23,27,37,43,47,53,67,73,81,83,103,107,113,137,157,163,167,
%T A240108 169,173,223,227,233,243,257,263,277,283,289,293,313,317,337,347,353,
%U A240108 367,383,397,433,443,463,467,487,503,529,547,557,563,587,593,607
%N A240108 Numbers with primitive root 20.
%H A240108 Vincenzo Librandi, <a href="/A240108/b240108.txt">Table of n, a(n) for n = 1..1000</a>
%t A240108 pr = 20; Select[Range[2, 700], MultiplicativeOrder[pr, #] == EulerPhi[#] &]
%t A240108 Join[{3,9,13,17},Select[Range[610],MemberQ[PrimitiveRootList[#],20]&]] (* _Harvey P. Dale_, Jul 17 2025 *)
%Y A240108 Cf. numbers with positive primitive root r: A167791 (r=2), A167792 (r=3), A167793 (r=5), A167794 (r=6), A167795 (r=7), A167796 (r=8), A167797 (r=10), A240028 (r=11), A240030 (r=12), A240032 (r=13), A240094 (r=14), A240096 (r=15), A240100 (r=17), A240103 (r=18), A240106 (r=19).
%Y A240108 Cf. numbers with negative primitive root r: A167798 (r=-2), A167799 (r=-3), A167800 (r=-4), A167801 (r=-5), A167802 (r=-6), A167803 (r=-7), A167804 (r=-8), A167805 (r=-9), A167806 (r=-10), A240029 (r=-11), A240031 (r=-12), A240093 (r=-13), A240095 (r=-14), A240097 (r=-15), A240100 (r=-17), A240102 (r=-18), A240104 (r=-19), A240107 (r=-20).
%K A240108 nonn
%O A240108 1,1
%A A240108 _Vincenzo Librandi_, Apr 01 2014