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 A301842 #4 Mar 27 2018 14:32:10 %S A301842 2,8,25,81,263,855,2778,9027,29333,95316,309725,1006437,3270370, %T A301842 10626915,34531665,112209036,364618033,1184809305,3849982618, %U A301842 12510339087,40651763813,132096011916,429239834325,1394794836717,4532320816850 %N A301842 Number of 2Xn 0..1 arrays with every element equal to 0, 1 or 2 horizontally or antidiagonally adjacent elements, with upper left element zero. %C A301842 Row 2 of A301841. %H A301842 R. H. Hardin, <a href="/A301842/b301842.txt">Table of n, a(n) for n = 1..210</a> %F A301842 Empirical: a(n) = 3*a(n-1) +a(n-2) -2*a(n-4) for n>6 %e A301842 Some solutions for n=5 %e A301842 ..0..1..1..0..0. .0..0..1..0..0. .0..0..0..1..1. .0..1..0..1..1 %e A301842 ..0..0..1..0..0. .0..0..0..1..1. .1..0..1..0..0. .1..1..0..0..0 %Y A301842 Cf. A301841. %K A301842 nonn %O A301842 1,1 %A A301842 _R. H. Hardin_, Mar 27 2018