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 A302681 #4 Apr 11 2018 12:29:13 %S A302681 4,4,8,12,18,40,94,184,358,760,1594,3220,6574,13636,28078,57460, %T A302681 118090,243232,499846,1026496,2110462,4339696,8918722,18329596, %U A302681 37680070,77455324,159200278,327229276,672635458,1382602264,2841890926,5841485128 %N A302681 Number of 3Xn 0..1 arrays with every element equal to 0, 1, 4 or 6 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero. %C A302681 Row 3 of A302680. %H A302681 R. H. Hardin, <a href="/A302681/b302681.txt">Table of n, a(n) for n = 1..210</a> %F A302681 Empirical: a(n) = a(n-1) +3*a(n-3) +3*a(n-4) for n>7 %e A302681 Some solutions for n=5 %e A302681 ..0..1..0..1..0. .0..1..1..1..0. .0..1..0..1..0. .0..0..0..1..0 %e A302681 ..0..1..0..1..0. .0..1..0..1..0. .0..1..1..1..0. .0..1..0..1..0 %e A302681 ..0..1..0..0..0. .0..1..0..1..0. .0..1..0..1..0. .0..1..1..1..0 %Y A302681 Cf. A302680. %K A302681 nonn %O A302681 1,1 %A A302681 _R. H. Hardin_, Apr 11 2018