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 A337858 #30 Mar 27 2024 21:12:48 %S A337858 3,5,37,101,44101,3766141,8122501,18671941,35772661,36969661, %T A337858 208168381,425420101,725862061,778003381,818423101,1269342901, %U A337858 9049716901,27221068981,60138957061,125980182901,137330493301,314912454781,315322826869,478543291381,667933881301 %N A337858 Integers k>=3 such that 2^k == 2 (mod k*(k-1)*(k-2)/6). %C A337858 Computed terms are prime. Is it always the case? If not it would be interesting to compute the smallest pseudoprime. %C A337858 It seems that all larger terms are of the form 180*k + 1, starting at a(5) = 44101 = 180*245 + 1. - _Hugo Pfoertner_, Sep 27 2020 %C A337858 Other terms of the form 180*k+1 (which are all prime): 60138957061, 125980182901, 137330493301, 478543291381, 667933881301, 700212813301, 701030830501, 720023604301, 766514618101, 778382658901. - _Chai Wah Wu_, Oct 06 2020 %H A337858 Delbert L. Johnson, <a href="/A337858/b337858.txt">Table of n, a(n) for n = 1..28</a> %t A337858 Select[Range[3, 10^7], PowerMod[2, #, #*(# - 1)*(# - 2)/6] == 2 &] (* _Amiram Eldar_, Sep 27 2020 *) %o A337858 (PARI) is(n) = n>=3 && Mod(2, n*(n-1)*(n-2)/6)^n ==2 %Y A337858 Cf. A337818, A337846. %K A337858 nonn %O A337858 1,1 %A A337858 _Benoit Cloitre_, Sep 26 2020 %E A337858 a(12)-a(18) from _Amiram Eldar_, Sep 27 2020 %E A337858 a(19)-a(25) from _Delbert L. Johnson_, Mar 27 2024