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 A212375 #17 Sep 08 2022 08:46:02
%S A212375 3,5,7,11,13,19,29,37,43,53,59,61,67,73,79,83,97,101,103,107,109,131,
%T A212375 139,149,151,157,163,173,179,181,193,197,199,211,227,229,241,251,269,
%U A212375 271,277,283,293,307,313,317,331,337,347,349,367,373,379,389,397
%N A212375 Primes p such that x^18 = 2 has no solution mod p.
%C A212375 Complement of A049550 relative to A000040.
%C A212375 This sequence is not the same as A040993. First disagreement at index 59: a(59)=433, A040993(59)=443.
%H A212375 Bruno Berselli, <a href="/A212375/b212375.txt">Table of n, a(n) for n = 1..1000</a>
%t A212375 Select[Prime[Range[PrimePi[500]]], ! MemberQ[PowerMod[Range[#], 18, #], Mod[2, #]] &]
%t A212375 ok[p_]:= Reduce[Mod[x^18 - 2, p] == 0, x, Integers] == False; Select[Prime[Range[80]], ok] (* _Vincenzo Librandi_, Sep 20 2012 *)
%o A212375 (Magma) [p: p in PrimesUpTo(500) | forall{x: x in ResidueClassRing(p) | x^18 ne 2}];
%o A212375 (Magma) [p: p in PrimesUpTo(400) | not exists{x : x in ResidueClassRing(p) | x^18 eq 2} ]; // _Vincenzo Librandi_, Sep 20 2012
%Y A212375 Cf. A000040, A049550.
%Y A212375 Cf. A040993.
%K A212375 nonn,easy
%O A212375 1,1
%A A212375 _Bruno Berselli_, Sep 13 2012