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 A042969 #10 Jun 26 2022 23:37:41
%S A042969 29,43,71,113,127,197,211,239,281,337,379,421,449,463,491,547,617,631,
%T A042969 659,673,701,743,827,911,953,967,1009,1051,1093,1163,1303,1373,1429,
%U A042969 1471,1499,1667,1709,1723,1933,2003,2017,2087,2129,2143
%N A042969 Primes p such that x^7 = 3 has no solution mod p.
%C A042969 Complement of A216881 relative to A000040. - _Vincenzo Librandi_, Sep 19 2012
%H A042969 Vincenzo Librandi, <a href="/A042969/b042969.txt">Table of n, a(n) for n = 1..1000</a>
%t A042969 ok[p_]:= Reduce[Mod[x^7 - 3, p] == 0, x, Integers] == False; Select[Prime[Range[800]], ok] (* _Vincenzo Librandi_, Sep 19 2012 *)
%o A042969 (Magma) [p: p in PrimesUpTo(2500) | not exists{x : x in ResidueClassRing(p) | x^7 eq 3} ]; // _Vincenzo Librandi_, Sep 19 2012
%K A042969 nonn,easy
%O A042969 1,1
%A A042969 _N. J. A. Sloane_