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=1..N} forms a (binary) heap if it satisfies a_i<a's wiki page.
{i=1..N} forms a (binary) heap if it satisfies a_i<a has authored 0 sequences.