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 A228501 #11 Sep 11 2018 09:45:51 %S A228501 2,3,12,29,88,239,684,1909,5392,15143,42644,119933,337512,949535, %T A228501 2671740,7517061,21150272,59508247,167433188,471090573,1325464216, %U A228501 3729333775,10492879052,29522830997,83065631600,233713998087,657579228980 %N A228501 Number of n X 3 binary arrays with top left value 1 and no two ones adjacent horizontally, vertically, diagonally or antidiagonally. %H A228501 R. H. Hardin, <a href="/A228501/b228501.txt">Table of n, a(n) for n = 1..210</a> %F A228501 Empirical: a(n) = 2*a(n-1) + 3*a(n-2) - 2*a(n-3). %F A228501 Empirical g.f.: x*(2 - x) / (1 - 2*x - 3*x^2 + 2*x^3). - _Colin Barker_, Sep 11 2018 %e A228501 Some solutions for n=4: %e A228501 ..1..0..1....1..0..0....1..0..1....1..0..0....1..0..0....1..0..1....1..0..0 %e A228501 ..0..0..0....0..0..1....0..0..0....0..0..0....0..0..0....0..0..0....0..0..1 %e A228501 ..0..0..1....0..0..0....0..0..1....1..0..1....0..0..0....0..1..0....0..0..0 %e A228501 ..0..0..0....1..0..0....1..0..0....0..0..0....0..0..1....0..0..0....0..0..0 %Y A228501 Column 3 of A228506. %K A228501 nonn %O A228501 1,1 %A A228501 _R. H. Hardin_, Aug 23 2013