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 A228502 #12 Sep 12 2018 06:13:29 %S A228502 3,5,29,87,358,1252,4749,17285,64235,236211,873250,3219652,11886927, %T A228502 43856285,161862005,597285195,2204231074,8134165648,30017792409, %U A228502 110774426621,408792375587,1508567655759,5567079710158,20544224979592 %N A228502 Number of n X 4 binary arrays with top left value 1 and no two ones adjacent horizontally, vertically, diagonally or antidiagonally. %H A228502 R. H. Hardin, <a href="/A228502/b228502.txt">Table of n, a(n) for n = 1..210</a> %F A228502 Empirical: a(n) = 2*a(n-1) + 7*a(n-2) - 2*a(n-3) - 3*a(n-4). %F A228502 Empirical g.f.: x*(1 - x)*(3 + 2*x) / (1 - 2*x - 7*x^2 + 2*x^3 + 3*x^4). - _Colin Barker_, Sep 12 2018 %e A228502 Some solutions for n=4: %e A228502 ..1..0..1..0....1..0..1..0....1..0..0..0....1..0..0..1....1..0..1..0 %e A228502 ..0..0..0..0....0..0..0..0....0..0..1..0....0..0..0..0....0..0..0..0 %e A228502 ..0..0..1..0....0..0..0..0....0..0..0..0....0..0..1..0....0..0..0..0 %e A228502 ..1..0..0..0....0..0..0..1....1..0..0..1....1..0..0..0....1..0..1..0 %Y A228502 Column 4 of A228506. %K A228502 nonn %O A228502 1,1 %A A228502 _R. H. Hardin_, Aug 23 2013