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.
(k>=0) = 2^(k-2)*(4 + Sum's wiki page.
(k>=0) = 2^(k-2)*(4 + Sum has authored 0 sequences.