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.
% 4) == 1 && is_square_free($'s wiki page.
% 4) == 1 && is_square_free($ has authored 0 sequences.