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 A185831 #9 Jul 22 2025 10:03:04 %S A185831 3,61,393,2398,15782,98975,649826,4143707,26679121,171597547, %T A185831 1102725806,7092378045,45590856963,293158517847,1884832244162, %U A185831 12118696565347,77918494954731,500981651046567,3221109348385647,20710370917938021 %N A185831 Half the number of nX5 binary arrays with every element equal to exactly one or two of its horizontal and vertical neighbors. %C A185831 Column 5 of A185835 %H A185831 R. H. Hardin, <a href="/A185831/b185831.txt">Table of n, a(n) for n = 1..200</a> %e A185831 Some solutions for 4X5 with a(1,1)=0 %e A185831 ..0..0..1..0..0....0..1..1..0..1....0..0..1..1..1....0..1..1..0..0 %e A185831 ..1..0..1..0..0....0..0..1..0..1....0..1..1..0..1....0..0..1..0..1 %e A185831 ..1..0..1..1..1....1..1..0..0..1....1..0..0..0..1....1..0..0..0..1 %e A185831 ..1..0..0..0..1....0..0..0..1..1....1..1..1..1..1....1..1..1..1..1 %K A185831 nonn %O A185831 1,1 %A A185831 _R. H. Hardin_ Feb 05 2011