A268634 Number of n X 3 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two exactly once.

12, 120, 840, 5178, 29772, 163878, 875592, 4578186, 23548164, 119570574, 600870336, 2993807250, 14810051580, 72819229974, 356173467576, 1734202809114, 8410141924596, 40641730213278, 195782548631472, 940481337385122

Offset: 1

Author

R. H. Hardin, Feb 09 2016

Keywords

• nonn

Examples

			Some solutions for n=6:
..0..0..0. .1..0..0. .1..0..0. .2..1..0. .0..1..2. .1..0..1. .1..0..0
..0..1..1. .0..1..0. .2..1..0. .1..0..0. .1..2..1. .0..1..0. .2..2..1
..0..0..0. .1..2..1. .1..0..0. .2..1..0. .2..2..1. .1..0..0. .2..1..0
..0..0..1. .2..2..2. .2..1..1. .2..0..0. .2..1..0. .2..1..0. .1..2..1
..0..1..0. .2..1..2. .1..2..2. .1..0..1. .1..2..1. .0..0..0. .2..2..2
..1..0..0. .0..0..1. .2..2..2. .2..1..0. .0..1..2. .0..0..0. .1..2..2
		

Links

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

Crossrefs

Column 3 of A268639.

Formula

Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4).

Empirical g.f.: 6*x*(2 - 2*x^2 + 3*x^3) / (1 - 5*x + 2*x^2)^2. - Colin Barker, Jan 14 2019