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 A216819 #15 Oct 19 2023 22:32:45 %S A216819 1,0,2,4,12,32,110,340,1209,4256,15974,60232 %N A216819 Number of simply 8-connected polyominoes of site-perimeter n. %H A216819 J. Fortier, A. Goupil, J. Lortie and J. Tremblay, <a href="https://doi.org/10.1016/j.tcs.2012.02.032">Exhaustive generation of gominoes</a>, Theoretical Computer Science, 502 (2013), 76-87. %Y A216819 Cf. A216818 (no holes), A216820 (any holes). %Y A216819 A342537 counts free (rather than fixed) polyominoes with given area (rather than site-perimeter). %K A216819 nonn,more %O A216819 4,3 %A A216819 _N. J. A. Sloane_, Sep 20 2012