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 A251121 #8 Jul 23 2025 13:05:55 %S A251121 10,40,108,266,580,1214,2420,4702,8926,16680,30766,56180,101734, %T A251121 182956,327080,581742,1030000,1816290,3191136,5588050,9755530, %U A251121 16983260,29489098 %N A251121 Number of (n+1)X(n+1) 0..1 arrays with no 2X2 subblock having the sum of its diagonal elements greater than the maximum of its antidiagonal elements. %C A251121 Diagonal of A251128 %e A251121 Some solutions for n=4 %e A251121 ..0..0..0..0..1....0..0..0..1..1....0..0..0..1..1....1..0..1..0..1 %e A251121 ..0..0..0..0..1....0..0..0..0..0....1..0..0..0..0....1..0..1..0..1 %e A251121 ..0..0..0..0..1....1..1..1..1..1....1..0..0..0..0....1..0..1..0..0 %e A251121 ..0..0..0..0..0....0..0..0..0..0....1..0..0..0..0....1..0..1..0..0 %e A251121 ..1..0..0..0..0....1..1..0..0..0....1..0..0..0..0....1..0..1..0..0 %K A251121 nonn %O A251121 1,1 %A A251121 _R. H. Hardin_, Nov 30 2014