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 A268784 #8 Jan 15 2019 09:14:23 %S A268784 2,17,72,302,1144,4207,14984,52335,179854,610504,2051436,6836258, %T A268784 22622554,74418562,243553160,793537401,2575357784,8329124488, %U A268784 26854438804,86342760711,276915214344,886094782671,2829527431748,9018299661270 %N A268784 Number of n X 3 binary arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two exactly once. %H A268784 R. H. Hardin, <a href="/A268784/b268784.txt">Table of n, a(n) for n = 1..210</a> %F A268784 Empirical: a(n) = 2*a(n-1) + 9*a(n-2) - 2*a(n-3) - 33*a(n-4) - 42*a(n-5) - 14*a(n-6) + 10*a(n-7) + 8*a(n-8) - a(n-10). %F A268784 Empirical g.f.: x*(2 + 13*x + 20*x^2 + 9*x^3 - 8*x^4 - 10*x^5 - 4*x^6) / ((1 + x)^2*(1 - 2*x - 3*x^2 - x^3 + x^4)^2). - _Colin Barker_, Jan 15 2019 %e A268784 Some solutions for n=4: %e A268784 ..1..0..1. .1..1..0. .1..0..0. .0..1..0. .1..0..0. .0..0..1. .1..0..1 %e A268784 ..0..1..0. .0..0..1. .0..0..1. .0..0..0. .1..0..1. .1..0..1. .0..1..0 %e A268784 ..0..0..0. .0..0..0. .1..0..0. .1..0..0. .0..0..0. .0..0..0. .0..0..1 %e A268784 ..1..0..0. .0..0..0. .1..0..0. .1..0..1. .0..1..0. .1..0..0. .0..0..0 %Y A268784 Column 3 of A268789. %K A268784 nonn %O A268784 1,1 %A A268784 _R. H. Hardin_, Feb 13 2016