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.
?SymmetricMatrixQ], {n, 5}], 1] (* _Eric W. Weisstein's wiki page.
?SymmetricMatrixQ], {n, 5}], 1] (* _Eric W. Weisstein has authored 0 sequences.