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 A207923 #9 Jul 22 2025 21:00:25 %S A207923 2,16,72,576,7744,138384,3773248,143233024,7961867964,694232238436, %T A207923 87251969161984,15584659071915024,4290136697951345984, %U A207923 1785288592992685527184,1059504761310616996153800 %N A207923 Number of n X n 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 0 0 and 1 1 1 vertically. %C A207923 Diagonal of A207928 %H A207923 R. H. Hardin, <a href="/A207923/b207923.txt">Table of n, a(n) for n = 1..19</a> %e A207923 Some solutions for n=5 %e A207923 ..0..0..1..1..1....1..0..0..1..1....1..0..1..1..1....0..0..1..1..1 %e A207923 ..0..0..1..1..0....1..0..1..1..0....1..0..0..1..1....0..1..1..0..0 %e A207923 ..1..1..0..0..1....0..1..1..0..1....0..1..1..0..0....1..0..0..1..1 %e A207923 ..0..0..1..1..0....1..0..0..1..1....0..0..1..1..0....0..0..1..1..1 %e A207923 ..1..0..1..1..1....1..1..1..0..0....1..1..0..0..1....1..1..1..0..0 %K A207923 nonn %O A207923 1,1 %A A207923 _R. H. Hardin_ Feb 21 2012