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 A203558 #8 Jul 22 2025 17:20:21 %S A203558 3,9,9,33,53,183,395,1249,3141,9459,25655,75639,212943,623093,1787609, %T A203558 5222369,15134933,44250051,128996855,377748883,1105350731,3242546393, %U A203558 9513228125,27953744695,82176836303,241834027353,712070156205 %N A203558 Number of nX2 0..2 arrays with row sums equal and column sums equal. %C A203558 Column 2 of A203564 %H A203558 R. H. Hardin, <a href="/A203558/b203558.txt">Table of n, a(n) for n = 1..210</a> %e A203558 Some solutions for n=5 %e A203558 ..1..1....2..2....2..0....2..2....0..0....1..1....1..1....2..0....0..0....2..2 %e A203558 ..1..1....2..2....1..1....2..2....0..0....0..2....0..2....1..1....0..0....2..2 %e A203558 ..2..0....2..2....1..1....2..2....0..0....2..0....2..0....2..0....0..0....2..2 %e A203558 ..1..1....2..2....1..1....2..2....0..0....2..0....0..2....0..2....0..0....2..2 %e A203558 ..0..2....2..2....0..2....2..2....0..0....0..2....2..0....0..2....0..0....2..2 %K A203558 nonn %O A203558 1,1 %A A203558 _R. H. Hardin_ Jan 03 2012