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 A317759 #4 Aug 06 2018 11:48:44 %S A317759 2,6,10,20,42,89,190,407,873,1874,4024,8642,18561,39866,85627,183917, %T A317759 395034,848492,1822474,3914489,8407926,18059375,38789713,83316386, %U A317759 178955184,384377666,825604417,1773314930,3808901427,8181135701 %N A317759 Number of nX2 0..1 arrays with every element unequal to 0, 1 or 2 horizontally, vertically or antidiagonally adjacent elements, with upper left element zero. %C A317759 Column 2 of A317764. %H A317759 R. H. Hardin, <a href="/A317759/b317759.txt">Table of n, a(n) for n = 1..210</a> %F A317759 Empirical: a(n) = 2*a(n-1) +a(n-2) -a(n-3) -a(n-4) for n>6 %e A317759 Some solutions for n=5 %e A317759 ..0..0. .0..1. .0..1. .0..0. .0..0. .0..0. .0..0. .0..0. .0..1. .0..0 %e A317759 ..1..1. .1..1. .1..1. .1..1. .1..1. .0..0. .0..1. .0..1. .1..1. .0..0 %e A317759 ..1..1. .0..0. .1..1. .1..0. .1..1. .0..0. .1..1. .1..1. .0..0. .1..1 %e A317759 ..0..0. .0..0. .1..1. .0..0. .1..1. .0..1. .0..0. .1..1. .0..1. .1..1 %e A317759 ..0..0. .1..1. .1..0. .0..1. .0..0. .1..1. .0..1. .1..0. .1..1. .0..0 %Y A317759 Cf. A317764. %K A317759 nonn %O A317759 1,1 %A A317759 _R. H. Hardin_, Aug 06 2018