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 A303677 #4 Apr 28 2018 09:19:58 %S A303677 2,5,7,17,31,49,103,193,327,641,1207,2129,4039,7585,13687,25585,47847, %T A303677 87425,162391,302609,556615,1031329,1916983,3538225,6550311,12155585, %U A303677 22474519,41599313,77121031,142707937,264156151,489441649,906031335 %N A303677 Number of nX2 0..1 arrays with every element unequal to 0, 1 or 3 king-move adjacent elements, with upper left element zero. %C A303677 Column 2 of A303682. %H A303677 R. H. Hardin, <a href="/A303677/b303677.txt">Table of n, a(n) for n = 1..210</a> %F A303677 Empirical: a(n) = a(n-1) +4*a(n-3) -2*a(n-4) for n>5 %e A303677 Some solutions for n=5 %e A303677 ..0..1. .0..1. .0..0. .0..0. .0..1. .0..1. .0..0. .0..0. .0..0. .0..0 %e A303677 ..0..0. .0..0. .1..0. .0..1. .1..1. .0..0. .1..0. .0..0. .0..0. .0..0 %e A303677 ..0..0. .0..0. .1..1. .1..1. .1..1. .0..0. .1..1. .0..0. .0..0. .0..0 %e A303677 ..0..0. .0..0. .1..1. .1..1. .0..1. .0..1. .0..0. .0..0. .0..0. .1..0 %e A303677 ..0..1. .0..0. .1..0. .1..0. .0..0. .1..1. .1..0. .0..0. .0..1. .1..1 %Y A303677 Cf. A303682. %K A303677 nonn %O A303677 1,1 %A A303677 _R. H. Hardin_, Apr 28 2018