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 A234012 #24 Aug 22 2020 15:53:55 %S A234012 1,4,24,230,2601,32810,433855,5923677,82675193,1173878266 %N A234012 Number of unbiased free polyominoes with 2n squares. %C A234012 Define the bias of a polyomino to be the difference between the number of black squares and the number of white squares when chessboard coloring is applied to the polyomino. Unbiased polyominoes are those having an equal number of black and white squares. The sequence is defined for 2n rather than n as odd-sized polyominoes are obviously biased. %H A234012 Herman Tulleken, <a href="https://www.researchgate.net/publication/333296614_Polyominoes">Polyominoes 2.2: How they fit together</a>, (2019). %Y A234012 Cf. A000105, A001933. %K A234012 nonn,more %O A234012 1,2 %A A234012 _John Mason_, Dec 18 2013 %E A234012 a(9)-a(10) from _Sean A. Irvine_, Aug 22 2020