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

1,1

Links

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

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

Example

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

Crossrefs

Column 3 of A228390.

Sequence in context: A328041 A242785 A359672 * A152801 A062297 A357791

Adjacent sequences: A228382 A228383 A228384 * A228386 A228387 A228388

Keyword

nonn

Author

R. H. Hardin, Aug 21 2013

Status

approved