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 A207839 #9 Jul 22 2025 20:52:20 %S A207839 2,16,72,780,10144,181896,5346600,235865752,13718515360,1274547293612, %T A207839 182632256870400,35910248805192512,10519355362828229320, %U A207839 4986223632232028372840,3295839087283933350008520 %N A207839 Number of n X n 0..1 arrays avoiding 0 0 0 and 0 0 1 horizontally and 0 0 0 and 1 1 1 vertically. %C A207839 Diagonal of A207845 %H A207839 R. H. Hardin, <a href="/A207839/b207839.txt">Table of n, a(n) for n = 1..22</a> %e A207839 Some solutions for n=4 %e A207839 ..1..0..1..1....1..0..1..0....0..1..1..1....0..1..1..1....1..0..1..0 %e A207839 ..1..0..1..1....0..1..0..0....1..0..1..0....1..0..1..1....1..1..0..1 %e A207839 ..0..1..0..0....1..1..1..1....1..1..0..1....0..1..0..0....0..1..1..1 %e A207839 ..0..1..0..0....1..0..1..0....0..1..1..1....1..1..1..0....1..0..1..0 %K A207839 nonn %O A207839 1,1 %A A207839 _R. H. Hardin_ Feb 21 2012