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 A269053 #7 Jan 18 2019 15:13:18 %S A269053 9,42,102,360,1068,3288,9864,29472,87312,257184,753504,2197632, %T A269053 6383808,18478464,53318784,153414144,440293632,1260710400,3602253312, %U A269053 10273007616,29245172736,83119822848,235886217216,668491456512,1892026552320 %N A269053 Number of 2 X n 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two not more than once. %H A269053 R. H. Hardin, <a href="/A269053/b269053.txt">Table of n, a(n) for n = 1..210</a> %F A269053 Empirical: a(n) = 4*a(n-1) - 8*a(n-3) - 4*a(n-4). %F A269053 Empirical g.f.: 3*x*(3 + 2*x - 22*x^2 + 8*x^3) / (1 - 2*x - 2*x^2)^2. - _Colin Barker_, Jan 18 2019 %e A269053 Some solutions for n=4: %e A269053 ..1..2..2..2. .2..1..2..1. .0..1..2..1. .1..0..0..1. .1..0..0..1 %e A269053 ..2..2..2..1. .2..1..0..0. .0..1..2..1. .0..1..0..0. .0..0..1..0 %Y A269053 Row 2 of A269052. %K A269053 nonn %O A269053 1,1 %A A269053 _R. H. Hardin_, Feb 18 2016