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 A210989 #8 Feb 16 2025 08:33:17 %S A210989 1,2,18,196,2500,33896,476270,6849777,100203194,1485200848, %T A210989 22245940545,336093325058,5114451441106,78306011677182, %U A210989 1205243866707468,18635412907198670,289296535756895985,4506983054619138245,70436637624668665265 %N A210989 Number of one-sided polyominoes with 2n-1 cells. %H A210989 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polyomino.html">Polyomino</a> %H A210989 Wikipedia, <a href="http://en.wikipedia.org/wiki/Polyomino">Polyomino</a> %Y A210989 Bisection of A000988. %Y A210989 Cf. A210988, A210997. %K A210989 nonn %O A210989 1,2 %A A210989 _Omar E. Pol_, Sep 16 2012