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 A128685 #19 Aug 10 2025 14:31:32 %S A128685 1,13,1027,52741,468481,2890927,4166539,37009999,228383233,999884119, %T A128685 1345997497,1900627417,2126334691,4499474941,5037873529,11728490839, %U A128685 104180336299,105897267463,150149565943,926550776281,4056529870783 %N A128685 Numbers k such that k^3 divides 12^(k^2) + 1. %C A128685 13 divides a(n) for n > 1. %t A128685 Select[Range[5*10^6], Mod[ 12^(#^2)+1, #^3]==0 &] (* _G. C. Greubel_, Jan 18 2018 *) %t A128685 Select[Range[5*10^6],PowerMod[12,#^2,#^3]==#^3-1&] (* The program generates the first 7 terms of the sequence. *) (* _Harvey P. Dale_, Aug 10 2025 *) %Y A128685 Cf. A127263, A128677, A128678, A128679, A128680, A128681, A128682, A128683, A128684. %K A128685 hard,nonn %O A128685 1,2 %A A128685 _Alexander Adamchuk_, Mar 31 2007 %E A128685 16 more terms from _Ryan Propper_, Dec 03 2007 %E A128685 Terms a(17) onward from _Max Alekseyev_, May 14 2010