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 A207874 #8 Jul 22 2025 20:54:28 %S A207874 2,16,72,400,1648,10742,51696,380632,2048344,17181610,99927528, %T A207874 1001175276,6019939360,76617072388,455429901920,7551993118538, %U A207874 45011858516784,1023575674079354,6041127787154280 %N A207874 Number of n X n 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 1 0 and 1 1 1 vertically. %C A207874 Diagonal of A207879 %e A207874 Some solutions for n=4 %e A207874 ..0..1..0..0....0..1..0..0....1..0..0..1....0..0..1..0....1..0..0..1 %e A207874 ..1..1..0..0....0..1..0..0....0..1..1..1....1..1..1..0....1..1..0..0 %e A207874 ..1..0..0..1....1..0..0..1....0..1..1..0....1..1..0..0....0..1..1..0 %e A207874 ..0..0..1..1....1..0..0..1....1..0..0..1....0..0..1..1....0..0..1..1 %K A207874 nonn %O A207874 1,1 %A A207874 _R. H. Hardin_ Feb 21 2012