A228385 Number of n X 3 binary arrays with top left value 1 and no two ones adjacent horizontally or vertically.

2, 5, 21, 72, 268, 963, 3513, 12732, 46274, 167977, 610085, 2215300, 8044836, 29213495, 106085921, 385237512, 1398945714, 5080103005, 18447794373, 66990969264, 243269759052, 883405230683, 3207981221305, 11649402857444

Offset: 1

Author

R. H. Hardin, Aug 21 2013

Keywords

• nonn

Examples

			Some solutions for n=4:
..1..0..1....1..0..0....1..0..1....1..0..0....1..0..0....1..0..1....1..0..0
..0..0..0....0..1..0....0..1..0....0..0..0....0..1..0....0..0..0....0..1..0
..0..0..1....1..0..0....1..0..0....0..0..0....1..0..0....1..0..1....0..0..0
..0..1..0....0..1..0....0..0..0....1..0..1....0..0..1....0..0..0....0..0..0
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210

Crossrefs

Column 3 of A228390.

Formula

Empirical: a(n) = 2*a(n-1) + 6*a(n-2) - a(n-4).

Empirical g.f.: x*(2 - x)*(1 + x) / (1 - 2*x - 6*x^2 + x^4). - Colin Barker, Sep 11 2018