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 A049555 #17 Jul 20 2025 06:30:56
%S A049555 2,3,5,7,11,13,17,19,23,29,31,37,41,43,53,59,61,67,71,73,79,83,89,97,
%T A049555 101,103,107,109,113,127,131,137,149,151,157,163,167,173,179,181,191,
%U A049555 193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,281,283
%N A049555 Primes p such that x^23 = 2 has a solution mod p.
%C A049555 Complement of A040984 relative to A000040. - _Vincenzo Librandi_, Sep 14 2012
%H A049555 R. J. Mathar, <a href="/A049555/b049555.txt">Table of n, a(n) for n = 1..1000</a>
%H A049555 <a href="/index/Pri#smp">Index entries for related sequences</a>
%e A049555 0^23 == 2 (mod 2). 2^23 == 2 (mod 3). 3^23 == 2 (mod 5). 4^23 == 2 (mod 7). 7^23 == 2 (mod 11). 7^23 == 2 (mod 13). 9^23 == 2 (mod 17). 15^23 == 2 (mod 19). 2^23 == 2 (mod 23). 18^23 == 2 (mod 29). 4^23 == 2 (mod 31). 13^23 == 2 (mod 37). 5^23 == 2 (mod 41). 27^23 == 2 (mod 43). - _R. J. Mathar_, Jul 20 2025
%t A049555 ok[p_]:= Reduce[Mod[x^23 - 2, p] == 0, x, Integers] =!= False; Select[Prime[Range[150]], ok] (* _Vincenzo Librandi_, Sep 14 2012 *)
%o A049555 (Magma) [p: p in PrimesUpTo(300) | exists(t){x : x in ResidueClassRing(p) | x^23 eq 2}]; // _Vincenzo Librandi_, Sep 14 2012
%Y A049555 Cf. A000040, A040984.
%K A049555 nonn,easy
%O A049555 1,1
%A A049555 _N. J. A. Sloane_