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 A268783 #8 Jan 15 2019 09:14:26 %S A268783 1,5,17,48,131,338,850,2091,5061,12095,28608,67095,156244,361652, %T A268783 832757,1908885,4358285,9915728,22489147,50862918,114743814,258261695, %U A268783 580072917,1300393467,2910078592,6501783407,14504787560,32313853992,71896385513 %N A268783 Number of n X 2 binary arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two exactly once. %H A268783 R. H. Hardin, <a href="/A268783/b268783.txt">Table of n, a(n) for n = 1..210</a> %F A268783 Empirical: a(n) = 2*a(n-1) + 3*a(n-2) - 2*a(n-3) - 6*a(n-4) - 4*a(n-5) - a(n-6). %F A268783 Empirical g.f.: x*(1 + 3*x + 4*x^2 + x^3) / (1 - x - 2*x^2 - x^3)^2. - _Colin Barker_, Jan 15 2019 %e A268783 Some solutions for n=4: %e A268783 ..1..0. .1..1. .0..0. .0..0. .0..0. .1..1. .0..0. .1..0. .0..0. .0..0 %e A268783 ..0..0. .0..0. .1..0. .1..1. .0..0. .0..0. .1..1. .1..0. .1..0. .0..1 %e A268783 ..0..1. .0..0. .1..0. .0..0. .1..1. .1..0. .0..0. .0..0. .0..1. .0..1 %e A268783 ..1..0. .0..1. .0..1. .1..0. .0..0. .0..1. .0..0. .0..1. .1..0. .0..0 %Y A268783 Column 2 of A268789. %K A268783 nonn %O A268783 1,2 %A A268783 _R. H. Hardin_, Feb 13 2016