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 A268887 #7 Jan 15 2019 17:31:47 %S A268887 0,5,14,54,158,475,1340,3740,10204,27521,73354,193842,508346,1324791, %T A268887 3433720,8858104,22757432,58253885,148634502,378142446,959527766, %U A268887 2429034323,6135877428,15469187604,38929330452,97806402617,245354321666 %N A268887 Number of 2 X n binary arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two exactly once. %H A268887 R. H. Hardin, <a href="/A268887/b268887.txt">Table of n, a(n) for n = 1..210</a> %F A268887 Empirical: a(n) = 2*a(n-1) + 5*a(n-2) - 4*a(n-3) - 11*a(n-4) - 6*a(n-5) - a(n-6). %F A268887 Empirical g.f.: x^2*(5 + 4*x + x^2) / ((1 + x)^2*(1 - 2*x - x^2)^2). - _Colin Barker_, Jan 15 2019 %e A268887 Some solutions for n=4: %e A268887 ..1..0..1..1. .1..1..0..0. .0..0..0..1. .1..0..0..0. .1..0..1..0 %e A268887 ..1..0..0..0. .0..1..0..1. .1..1..0..0. .0..1..1..0. .0..1..0..0 %Y A268887 Row 2 of A268886. %K A268887 nonn %O A268887 1,2 %A A268887 _R. H. Hardin_, Feb 15 2016