cp's OEIS Frontend

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.

A049556 Primes p such that x^24 = 2 has a solution mod p.

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%I A049556 #17 Jul 20 2025 08:17:58
%S A049556 2,23,31,47,71,89,127,167,191,223,233,239,257,263,311,359,383,431,439,
%T A049556 479,503,599,601,647,719,727,743,839,863,881,887,911,919,983,1031,
%U A049556 1103,1151,1217,1223,1289,1319,1327,1367,1399,1423,1433,1439,1471,1487,1511
%N A049556 Primes p such that x^24 = 2 has a solution mod p.
%C A049556 Complement of A059362 relative to A000040. - _Vincenzo Librandi_, Sep 14 2012
%H A049556 R. J. Mathar, <a href="/A049556/b049556.txt">Table of n, a(n) for n = 1..1000</a>
%H A049556 <a href="/index/Pri#smp">Index entries for related sequences</a>
%e A049556 0^24 == 2 (mod 2). 5^24 == 2 (mod 23). 3^24 == 2 (mod 31). 2^24 == 2 (mod 47). 24^24 == 2 (mod 71). 25^24 == 2 (mod 89). 5^24 == 2 (mod 127). 63^24 == 2 (mod 167). - _R. J. Mathar_, Jul 20 2025
%t A049556 ok[p_]:= Reduce[Mod[x^24 - 2, p] == 0, x, Integers] =!= False; Select[Prime[Range[300]], ok] (* _Vincenzo Librandi_, Sep 14 2012 *)
%o A049556 (Magma) [p: p in PrimesUpTo(1600) | exists(t){x : x in ResidueClassRing(p) | x^24 eq 2}]; // _Vincenzo Librandi_, Sep 14 2012
%Y A049556 Cf. A000040, A059362.
%K A049556 nonn,easy
%O A049556 1,1
%A A049556 _N. J. A. Sloane_