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 A268744 #7 Mar 21 2018 11:38:43 %S A268744 4,11,32,89,244,659,1760,4657,12228,31899,82752,213641,549236,1406755, %T A268744 3591232,9140833,23204612,58765099,148496608,374496953,942729588, %U A268744 2369172915,5944748064,14895231121,37272007108,93149401019,232527917312 %N A268744 Number of n X 2 binary arrays with some element plus some horizontally or vertically adjacent neighbor totalling two no more than once. %C A268744 Column 2 of A268750. %H A268744 R. H. Hardin, <a href="/A268744/b268744.txt">Table of n, a(n) for n = 1..210</a> %F A268744 Empirical: a(n) = 4*a(n-1) - 2*a(n-2) - 4*a(n-3) - a(n-4). %F A268744 Empirical g.f.: x*(4 - 5*x - 4*x^2 - x^3) / (1 - 2*x - x^2)^2. - _Colin Barker_, Mar 21 2018 %e A268744 Some solutions for n=4: %e A268744 ..0..0. .1..0. .0..0. .0..0. .0..0. .0..0. .1..0. .0..1. .1..0. .0..1 %e A268744 ..1..0. .0..1. .1..0. .0..0. .1..1. .0..0. .1..0. .0..0. .0..0. .0..0 %e A268744 ..1..0. .0..0. .1..0. .0..0. .0..0. .1..0. .0..1. .0..1. .1..0. .0..1 %e A268744 ..0..0. .1..1. .0..1. .0..1. .1..0. .0..0. .0..0. .1..0. .1..0. .0..0 %Y A268744 Cf. A268750. %K A268744 nonn %O A268744 1,1 %A A268744 _R. H. Hardin_, Feb 12 2016