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 A185829 #9 Jul 22 2025 10:02:50 %S A185829 1,10,30,118,393,1430,5004,17877,63181,224324,794939,2819380,9995857, %T A185829 35445025,125677385,445630567,1580102608,5602722348,19866041906, %U A185829 70440800557,249768066156,885624613914,3140236676877,11134612682393 %N A185829 Half the number of nX3 binary arrays with every element equal to exactly one or two of its horizontal and vertical neighbors. %C A185829 Column 3 of A185835 %H A185829 R. H. Hardin, <a href="/A185829/b185829.txt">Table of n, a(n) for n = 1..200</a> %F A185829 Empirical: a(n)=2*a(n-1)+6*a(n-2)-a(n-3)-3*a(n-4)+4*a(n-5)-4*a(n-6)-32*a(n-7)-9*a(n-8)-4*a(n-9)-19*a(n-10)+17*a(n-11)+3*a(n-12)+a(n-13)-a(n-14) %e A185829 Some solutions for 4X3 with a(1,1)=0 %e A185829 ..0..1..1....0..0..0....0..0..0....0..0..1....0..1..1....0..0..0....0..0..0 %e A185829 ..0..0..0....1..1..0....1..1..1....1..1..1....0..0..0....0..1..1....0..1..0 %e A185829 ..1..1..1....0..0..1....0..0..1....1..0..0....1..1..0....0..1..0....0..1..0 %e A185829 ..0..0..1....0..1..1....0..0..1....1..1..1....0..0..0....0..0..0....0..1..0 %K A185829 nonn %O A185829 1,2 %A A185829 _R. H. Hardin_ Feb 05 2011