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 A301786 #4 Mar 26 2018 16:38:56 %S A301786 5,9,17,32,61,116,221,421,802,1528,2911,5546,10566,20130,38351,73065, %T A301786 139201,265201,505252,962589,1833892,3493869,6656401,12681550, %U A301786 24160460,46029691,87694210,167072042,318300002,606414395,1155320189,2201076937 %N A301786 Number of nX4 0..1 arrays with every element equal to 0 or 1 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301786 Column 4 of A301790. %H A301786 R. H. Hardin, <a href="/A301786/b301786.txt">Table of n, a(n) for n = 1..210</a> %F A301786 Empirical: a(n) = a(n-1) +2*a(n-2) -a(n-4) %e A301786 Some solutions for n=5 %e A301786 ..0..0..1..0. .0..1..0..1. .0..1..0..1. .0..1..1..0. .0..0..1..0 %e A301786 ..1..0..1..0. .1..0..1..0. .0..1..0..1. .0..0..1..0. .1..0..1..1 %e A301786 ..1..0..1..0. .1..0..1..1. .0..1..0..1. .1..0..1..0. .1..0..0..1 %e A301786 ..1..0..1..0. .1..0..0..1. .0..1..0..1. .0..1..0..1. .1..1..0..0 %e A301786 ..1..0..1..1. .1..1..0..1. .0..1..0..0. .0..1..0..1. .0..1..1..0 %Y A301786 Cf. A301790. %K A301786 nonn %O A301786 1,1 %A A301786 _R. H. Hardin_, Mar 26 2018