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 A269031 #8 Jan 18 2019 09:58:05 %S A269031 36,216,2166,18384,146064,1114848,8277072,60218112,431354928, %T A269031 3052215072,21383561232,148585984320,1025363155440,7034327057760, %U A269031 48013557090768,326276117933952,2208609401649072,14899002865010592,100198549907000208 %N A269031 Number of n X 4 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two exactly once. %H A269031 R. H. Hardin, <a href="/A269031/b269031.txt">Table of n, a(n) for n = 1..210</a> %F A269031 Empirical: a(n) = 14*a(n-1) - 57*a(n-2) + 56*a(n-3) - 16*a(n-4) for n>5. %F A269031 Empirical g.f.: 6*x*(6 - 48*x + 199*x^2 - 274*x^3 + 105*x^4) / (1 - 7*x + 4*x^2)^2. - _Colin Barker_, Jan 18 2019 %e A269031 Some solutions for n=4: %e A269031 ..0..0..0..1. .1..0..0..1. .0..1..2..1. .2..1..0..0. .2..2..1..2 %e A269031 ..0..1..0..1. .1..0..0..0. .2..1..0..1. .2..1..0..1. .2..2..2..1 %e A269031 ..2..1..2..2. .0..0..1..0. .0..1..0..1. .2..1..0..1. .2..1..2..2 %e A269031 ..2..1..2..2. .0..1..0..0. .2..1..2..0. .2..1..2..2. .2..1..2..2 %Y A269031 Column 4 of A269035. %K A269031 nonn %O A269031 1,1 %A A269031 _R. H. Hardin_, Feb 18 2016