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 A269146 #8 Jan 19 2019 12:08:35 %S A269146 4,80,768,6224,46464,330192,2270592,15251152,100647168,655139152, %T A269146 4217820672,26911075152,170416738944,1072338720464,6710943646848, %U A269146 41800542176720,259288295447040,1602497927690832,9871915467776256 %N A269146 Number of n X 2 0..3 arrays with some element plus some horizontally, antidiagonally or vertically adjacent neighbor totalling three exactly once. %H A269146 R. H. Hardin, <a href="/A269146/b269146.txt">Table of n, a(n) for n = 1..210</a> %F A269146 Empirical: a(n) = 12*a(n-1) - 38*a(n-2) + 12*a(n-3) - a(n-4) for n>5. %F A269146 Empirical g.f.: 4*x*(1 - x)*(1 + 9*x - x^2 - x^3) / (1 - 6*x + x^2)^2. - _Colin Barker_, Jan 19 2019 %e A269146 Some solutions for n=4: %e A269146 ..3..2. .0..0. .2..0. .3..3. .1..0. .1..0. .1..3. .3..1. .0..2. .1..1 %e A269146 ..2..0. .2..3. .0..2. .3..3. .1..1. .0..2. .0..1. .1..0. .0..0. .3..3 %e A269146 ..1..0. .2..2. .0..3. .1..0. .1..3. .0..0. .0..0. .0..1. .2..3. .3..2 %e A269146 ..0..1. .3..3. .2..3. .0..0. .1..0. .1..3. .2..0. .0..2. .3..3. .0..2 %Y A269146 Column 2 of A269152. %K A269146 nonn %O A269146 1,1 %A A269146 _R. H. Hardin_, Feb 20 2016