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 A210986 #13 Feb 16 2025 08:33:17
%S A210986 2,19,216,2725,36446,505861,7204874,104592937,1540820542,22964779660,
%T A210986 345532572678,5239988770268,79992676367108,1228088671826973,
%U A210986 18946775782611174,293560133910477776,4565553929115769162,71242712815411950635
%N A210986 Number of fixed polyominoes with 2n cells.
%H A210986 Jean-François Alcover, <a href="/A210986/b210986.txt">Table of n, a(n) for n = 1..28</a>
%H A210986 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polyomino.html">Polyomino</a>
%H A210986 Wikipedia, <a href="http://en.wikipedia.org/wiki/Polyomino">Polyomino</a>
%F A210986 a(n) = A001168(2*n).
%t A210986 A001168 = Cases[Import["https://oeis.org/A001168/b001168.txt", "Table"], {_, _}][[All, 2]];
%t A210986 a[n_] := A001168[[2 n]];
%t A210986 a /@ Range[1, Length[A001168]/2 // Floor] (* _Jean-François Alcover_, Sep 22 2019 *)
%Y A210986 Bisection of A001168.
%Y A210986 Cf. A210987, A210988, A210996,
%K A210986 nonn
%O A210986 1,1
%A A210986 _Omar E. Pol_, Sep 16 2012