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 A268991 #8 Jan 17 2019 17:20:50 %S A268991 13,103,805,6009,43512,308112,2144780,14730784,100087792,674045392, %T A268991 4505925696,29933341056,197782652096,1300744853760,8519586895104, %U A268991 55600022810880,361688403251200,2346083095244800,15178387509332992 %N A268991 Number of n X 4 binary arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once. %H A268991 R. H. Hardin, <a href="/A268991/b268991.txt">Table of n, a(n) for n = 1..210</a> %F A268991 Empirical: a(n) = 16*a(n-1) - 88*a(n-2) + 200*a(n-3) - 208*a(n-4) + 96*a(n-5) - 16*a(n-6) for n>7. %F A268991 Empirical g.f.: x*(13 - 105*x + 301*x^2 - 407*x^3 + 312*x^4 - 112*x^5 + 4*x^6) / (1 - 8*x + 12*x^2 - 4*x^3)^2. - _Colin Barker_, Jan 17 2019 %e A268991 Some solutions for n=4: %e A268991 ..0..1..0..0. .1..0..0..0. .0..1..0..1. .0..0..0..0. .1..0..0..1 %e A268991 ..0..1..0..0. .1..0..1..0. .0..0..0..0. .1..0..1..0. .1..1..0..1 %e A268991 ..1..0..0..1. .1..0..1..0. .0..0..0..1. .0..1..0..0. .0..0..0..1 %e A268991 ..1..0..0..0. .1..0..0..0. .1..0..0..1. .0..0..0..0. .0..0..0..1 %Y A268991 Column 4 of A268995. %K A268991 nonn %O A268991 1,1 %A A268991 _R. H. Hardin_, Feb 17 2016