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 A055689 #14 Jul 11 2021 14:15:40
%S A055689 2,38,16987850,2416266950,5995229030,7193673830,11465419550,
%T A055689 17783484530,72155530502,142013229530,174523785590,189282539138,
%U A055689 294183810998,302690164298,354613312130,774557575610,933821938790,1407294504938,1974020768390,2112969494570,2878251281402,3239815009970,3756030401750,3915556797110,6086837726270,6154479362702,6760841132870,7412805544190,7430816963570,10197159330050,12162461471270,15374128532210,15561152727890,17132853402170,17728631282570,25843631671550,38138222902514,39974191417010,56482483860710,71475592618370,78107027121482
%N A055689 Numbers k such that 6^k == -1 (mod k-1).
%t A055689 Do[If[PowerMod[6, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]
%K A055689 nonn
%O A055689 1,1
%A A055689 _Robert G. Wilson v_, Jun 09 2000
%E A055689 Terms a(4) onward from _Max Alekseyev_, Oct 12 2012