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 A227160 #7 Jul 23 2025 05:34:33 %S A227160 2,8,62,944,37012,3754497,1009485843,732609096798 %N A227160 Number of n X n 0,1 arrays indicating 2X2 subblocks of some larger (n+1)X(n+1) binary array having a sum of one or less, with rows and columns of the latter in lexicographically nondecreasing order. %C A227160 Diagonal of A227165 %e A227160 Some solutions for n=4 %e A227160 ..1..1..1..0....1..1..0..0....1..1..0..0....1..1..0..0....1..0..0..0 %e A227160 ..1..1..0..0....1..0..0..0....1..0..0..1....1..0..0..0....0..1..1..1 %e A227160 ..0..0..1..1....1..0..1..1....0..0..1..1....0..0..0..1....0..1..1..1 %e A227160 ..0..0..0..1....0..1..1..0....0..1..1..1....0..1..0..0....0..0..1..0 %K A227160 nonn %O A227160 1,1 %A A227160 _R. H. Hardin_ Jul 03 2013