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 A210987 #11 Feb 16 2025 08:33:17 %S A210987 1,6,63,760,9910,135268,1903890,27394666,400795844,5940738676, %T A210987 88983512783,1344372335524,20457802016011,313224032098244, %U A210987 4820975409710116,74541651404935148,1157186142148293638,18027932215016128134 %N A210987 Number of fixed polyominoes with 2n-1 cells. %H A210987 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polyomino.html">Polyomino</a> %H A210987 Wikipedia, <a href="http://en.wikipedia.org/wiki/Polyomino">Polyomino</a> %F A210987 a(n) = A001168(2*n-1). %Y A210987 Bisection of A001168. %Y A210987 Cf. A210986, A210989, A210997. %K A210987 nonn %O A210987 1,2 %A A210987 _Omar E. Pol_, Sep 16 2012