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 A175866 #10 Aug 20 2023 21:04:27 %S A175866 5,13,19,173,5501 %N A175866 Numbers k such that 2^(k-1) == 1 (mod k) and 2^(k-1) == 3*k + 1 (mod k^2). %Y A175866 Cf. A124924. %K A175866 nonn,more %O A175866 1,1 %A A175866 _Alzhekeyev Ascar M_, Sep 30 2010