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 A338213 #7 Oct 18 2020 06:05:23 %S A338213 1,0,0,0,0,1,0,0,1,0,1,1,3,2,4,6,13,15,30,50,93,158,287,513,950,1735, %T A338213 3212,5945,11099,20720,38910,73002,137821,259757 %N A338213 a(n) is the number of free polyominoes with sprawl n. %C A338213 The sprawl of a polyomino is the number of cells in a polyomino plus the number of cells adjacent to it. %H A338213 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a338/A338213.java">Java program</a> (github) %F A338213 Antidiagonal sums of A338211. %Y A338213 Cf. A000105, A338211, A338212. %K A338213 nonn,more %O A338213 0,13 %A A338213 _Sean A. Irvine_ and _Allan C. Wechsler_, Oct 17 2020