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 A207515 #9 Jul 22 2025 20:31:56 %S A207515 2,16,98,1307,29622,1048423,54373655,4964342828,715483286848, %T A207515 161734351034666,59741686819322041,35917251659399987384, %U A207515 34508253720326500890077,53717705561862882229716065 %N A207515 Number of n X n 0..1 arrays avoiding 0 0 1 and 0 1 0 horizontally and 0 1 0 and 1 0 1 vertically. %C A207515 Diagonal of A207519 %H A207515 R. H. Hardin, <a href="/A207515/b207515.txt">Table of n, a(n) for n = 1..16</a> %e A207515 Some solutions for n=4 %e A207515 ..1..0..0..0....1..1..0..1....0..0..0..0....0..1..1..0....0..1..1..0 %e A207515 ..1..1..0..1....1..1..0..1....1..1..1..0....1..1..0..0....0..1..1..1 %e A207515 ..0..1..1..1....0..1..1..0....1..1..1..0....1..0..0..0....1..0..1..1 %e A207515 ..0..1..1..0....0..1..1..0....1..1..0..1....0..0..0..0....1..0..1..1 %K A207515 nonn %O A207515 1,1 %A A207515 _R. H. Hardin_ Feb 18 2012