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 A243221 #10 Aug 15 2021 18:35:23 %S A243221 1,1,4,44,2593,407620,333518324,696849783788,7561681603209033, %T A243221 204785162442300693673,28874426647917459828127044, %U A243221 10023323177854055068860282476760,18172145684566998309243670369029131178,80387219406473992671391703779030095453926416 %N A243221 Number of quarter-square matchings of the n X n grid graph. %C A243221 Number of ways floor(n^2/4) dominoes can be placed on an n X n chessboard. a(n) is the central term in the n-th row of A242861. %H A243221 Alois P. Heinz, <a href="/A243221/b243221.txt">Table of n, a(n) for n = 0..14</a> %F A243221 a(n) = A242861(n,floor(n^2/4)) = A242861(n,A002620(n)). %Y A243221 Cf. A002620, A242861. %K A243221 nonn %O A243221 0,3 %A A243221 _Alois P. Heinz_, Jun 01 2014