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 A228385 #11 Sep 11 2018 05:41:16 %S A228385 2,5,21,72,268,963,3513,12732,46274,167977,610085,2215300,8044836, %T A228385 29213495,106085921,385237512,1398945714,5080103005,18447794373, %U A228385 66990969264,243269759052,883405230683,3207981221305,11649402857444 %N A228385 Number of n X 3 binary arrays with top left value 1 and no two ones adjacent horizontally or vertically. %H A228385 R. H. Hardin, <a href="/A228385/b228385.txt">Table of n, a(n) for n = 1..210</a> %F A228385 Empirical: a(n) = 2*a(n-1) + 6*a(n-2) - a(n-4). %F A228385 Empirical g.f.: x*(2 - x)*(1 + x) / (1 - 2*x - 6*x^2 + x^4). - _Colin Barker_, Sep 11 2018 %e A228385 Some solutions for n=4: %e A228385 ..1..0..1....1..0..0....1..0..1....1..0..0....1..0..0....1..0..1....1..0..0 %e A228385 ..0..0..0....0..1..0....0..1..0....0..0..0....0..1..0....0..0..0....0..1..0 %e A228385 ..0..0..1....1..0..0....1..0..0....0..0..0....1..0..0....1..0..1....0..0..0 %e A228385 ..0..1..0....0..1..0....0..0..0....1..0..1....0..0..1....0..0..0....0..0..0 %Y A228385 Column 3 of A228390. %K A228385 nonn %O A228385 1,1 %A A228385 _R. H. Hardin_, Aug 21 2013