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 A268989 #8 Jan 17 2019 17:20:39 %S A268989 4,13,41,126,379,1121,3272,9449,27049,76866,217079,609793,1705036, %T A268989 4748101,13174889,36440646,100503667,276476129,758785424,2078056481, %U A268989 5680052329,15497929098,42216552431,114824352001,311871557524 %N A268989 Number of n X 2 binary arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once. %H A268989 R. H. Hardin, <a href="/A268989/b268989.txt">Table of n, a(n) for n = 1..210</a> %F A268989 Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3) - a(n-4). %F A268989 Empirical g.f.: x*(4 - 11*x + 7*x^2 - x^3) / (1 - 3*x + x^2)^2. - _Colin Barker_, Jan 17 2019 %e A268989 Some solutions for n=4: %e A268989 ..1..0. .1..1. .1..0. .0..0. .1..0. .1..1. .0..0. .1..0. .0..0. .1..1 %e A268989 ..0..1. .0..0. .0..1. .1..0. .1..0. .0..0. .0..0. .0..0. .1..0. .0..1 %e A268989 ..0..1. .1..0. .0..0. .1..0. .0..0. .1..0. .0..1. .1..0. .0..0. .0..0 %e A268989 ..1..0. .1..0. .1..0. .0..1. .0..1. .0..0. .1..0. .0..1. .1..1. .1..0 %Y A268989 Column 2 of A268995. %K A268989 nonn %O A268989 1,1 %A A268989 _R. H. Hardin_, Feb 17 2016