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 A130866 #20 Apr 15 2023 15:43:21
%S A130866 1,2,4,9,21,56,164,533,1818,6473,23546,87146,325737,1227708,4654284,
%T A130866 17733539,67841448,260463500,1003087732,3873759682,14996820360,
%U A130866 58188678048,226235685776,881235386179,3438462430943,13437551253018
%N A130866 Number of polyominoes (or square animals) with at most n cells.
%C A130866 The sequence excludes the null polyomino of size 0. - _John Mason_, Jan 10 2023
%H A130866 John Mason, <a href="/A130866/b130866.txt">Table of n, a(n) for n = 1..50</a>
%F A130866 a(n) = Sum_{k=1..n} A000105(k). - _John Mason_, Jan 10 2023
%F A130866 a(n) = A173271(n) - 1. - _John Mason_, Feb 21 2023
%Y A130866 Partial sums of A000105 starting from A000105(1). Cf. A173271.
%K A130866 nonn
%O A130866 1,2
%A A130866 _Tanya Khovanova_, Jul 23 2007
%E A130866 Offset corrected by _John Mason_, Jan 10 2023