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 A337859 #16 Oct 12 2020 00:30:59 %S A337859 3,5,37,44101,157081,2031121,7282801,8122501,18671941,78550201, %T A337859 208168381,770810041,2658625201,2710529641,5241663001,14643783001, %U A337859 18719308441,56181482281,73303609681,74623302001,110102454001,140659081201 %N A337859 k-1 for integers k>=4 such that 2^k == 4 (mod k*(k-1)*(k-2)*(k-3)/24). %C A337859 Computed terms are prime. Is it always the case? Probably not and it would be interesting to compute the smallest pseudoprime. %C A337859 It seems that all larger terms are of the form 60*k + 1, starting at a(4) = 44101 = 60*735 + 1. Further terms of this form after a(17) are 56181482281, 73303609681, 74623302001, 110102454001, 140659081201, 283268822761, 469078212241, 530106748081, 570417709681, 701030830501, 720023604301; all are prime. - _Hugo Pfoertner_, Sep 28 2020 %t A337859 Select[Range[4, 10^7], (t = #*(# - 1)*(# - 2)*(# - 3)/24) == 1 || PowerMod[2, #, t] == 4 &] - 1 (* _Amiram Eldar_, Sep 27 2020 *) %o A337859 (PARI) is(k) = k>=4 && Mod(2,k*(k-1)*(k-2)*(k-3)/24)^k == 4 %Y A337859 Cf. A337818, A337846. %K A337859 nonn,more %O A337859 1,1 %A A337859 _Benoit Cloitre_, Sep 26 2020 %E A337859 a(13)-a(17) from _Amiram Eldar_, Sep 27 2020 %E A337859 a(18)-a(22) from _Chai Wah Wu_, Oct 09 2020