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 A055693 #11 Jul 11 2021 15:32:55
%S A055693 2,102,41310,102690,309162,315150,1000002,2488530,4564350,12679002,
%T A055693 17166870,28855610,35049930,38982870,42176490,43232070,53288510,
%U A055693 64253070,104439090,126446850,130659210,144379602,208313490,252852390,284335410,284397750,337122750,379257930,385659630
%N A055693 Numbers k such that 10^k == -1 (mod k-1).
%t A055693 Do[If[PowerMod[10, n, n-1]==n-2, Print[n]], {n, 2, 10^8}]
%K A055693 nonn
%O A055693 1,1
%A A055693 _Robert G. Wilson v_, Jun 09 2000
%E A055693 Corrected and extended by _Max Alekseyev_, Oct 12 2012