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 A207711 #9 Jul 22 2025 20:42:27 %S A207711 2,16,114,2205,97580,10150118,2433018665,1332236625328, %T A207711 1658417176295910,4680320299339768945,29900757895299392674248, %U A207711 432064042048194196301219286,14114419978195735103237247653751,1042092211595049585701702108677740928 %N A207711 Number of n X n 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 1 and 1 0 0 vertically. %C A207711 Diagonal of A207717 %H A207711 R. H. Hardin, <a href="/A207711/b207711.txt">Table of n, a(n) for n = 1..20</a> %e A207711 Some solutions for n=4 %e A207711 ..1..0..1..0....1..0..1..0....1..0..1..0....0..1..1..0....0..1..0..1 %e A207711 ..1..1..0..1....1..0..1..0....0..1..0..0....1..1..0..0....1..1..1..0 %e A207711 ..0..1..1..1....1..0..1..0....1..1..1..0....1..1..1..0....0..1..0..1 %e A207711 ..1..1..1..1....1..0..1..0....0..1..1..0....0..1..1..0....1..0..1..1 %K A207711 nonn %O A207711 1,1 %A A207711 _R. H. Hardin_ Feb 19 2012