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 A055690 #13 Jul 23 2021 05:25:24
%S A055690 2,3,5,6,9,26,45,66,87,345,765,906,3926,8405,11766,23805,35145,42966,
%T A055690 59685,95289,317250,413325,416757,722745,770066,890825,938457,1325826,
%U A055690 1921986,3315378,3675555,5299250,6791445,6899685,9371826,10892313
%N A055690 Numbers k such that 7^k == -1 (mod k-1).
%H A055690 Amiram Eldar, <a href="/A055690/b055690.txt">Table of n, a(n) for n = 1..285</a>
%t A055690 Do[If[PowerMod[7, n, n-1]==n-2, Print[n]], {n, 2, 2*10^7}]
%Y A055690 Cf. A055685, A055686, A055687, A055688, A055689, A055691, A055692, A055693, A055694, A055695.
%K A055690 nonn
%O A055690 1,1
%A A055690 _Robert G. Wilson v_, Jun 09 2000