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 A049557 #17 Jul 20 2025 07:22:32
%S A049557 2,3,5,7,13,17,19,23,29,37,43,47,53,59,67,73,79,83,89,97,103,107,109,
%T A049557 113,127,137,139,149,157,163,167,173,179,193,197,199,223,227,229,233,
%U A049557 239,241,257,263,269,277,283,293,307,313,317,337,347,349,353,359,367
%N A049557 Primes p such that x^25 = 2 has a solution mod p.
%C A049557 Complement of A059313 relative to A000040. - _Vincenzo Librandi_, Sep 14 2012
%H A049557 R. J. Mathar, <a href="/A049557/b049557.txt">Table of n, a(n) for n = 1..1000</a>
%H A049557 <a href="/index/Pri#smp">Index entries for related sequences</a>
%e A049557 0^25 == 2 (mod 2). 2^25 == 2 (mod 3). 2^25 == 2 (mod 5). 2^25 == 2 (mod 7). 2^25 == 2 (mod 13). 2^25 == 2 (mod 17). 3^25 == 2 (mod 19). 16^25 == 2 (mod 23). 19^25 == 2 (mod 29). 15^25 == 2 (mod 37). - _R. J. Mathar_, Jul 20 2025
%t A049557 ok[p_]:= Reduce[Mod[x^25 - 2, p] == 0, x, Integers] =!= False; Select[Prime[Range[100]], ok] (* _Vincenzo Librandi_, Sep 14 2012 *)
%o A049557 (Magma) [p: p in PrimesUpTo(400) | exists(t){x : x in ResidueClassRing(p) | x^25 eq 2}]; // _Vincenzo Librandi_, Sep 14 2012
%Y A049557 Cf. A000040, A059313.
%K A049557 nonn,easy
%O A049557 1,1
%A A049557 _N. J. A. Sloane_