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 A207494 #9 Jul 22 2025 20:30:01 %S A207494 2,16,102,1004,14253,237576,5715255,163471950,6200122170,294261603282, %T A207494 17977383927693,1375335087129521,138833395825965196, %U A207494 17233401412131428885,2924391663494366576782,600552802391087361313757 %N A207494 Number of n X n 0..1 arrays avoiding 0 0 0 and 0 1 1 horizontally and 0 0 1 and 1 0 0 vertically. %C A207494 Diagonal of A207500 %H A207494 R. H. Hardin, <a href="/A207494/b207494.txt">Table of n, a(n) for n = 1..18</a> %e A207494 Some solutions for n=4 %e A207494 ..1..1..0..1....0..0..1..0....1..1..0..1....0..1..0..0....1..1..0..1 %e A207494 ..0..1..0..0....1..1..1..1....1..1..0..1....0..0..1..0....0..0..1..0 %e A207494 ..1..1..0..1....0..0..1..0....0..1..0..0....0..1..0..0....1..1..1..1 %e A207494 ..0..1..0..1....1..1..0..1....1..0..0..1....0..0..1..0....1..0..1..0 %K A207494 nonn %O A207494 1,1 %A A207494 _R. H. Hardin_ Feb 18 2012