A269180 Number of n X 2 0..3 arrays with some element plus some horizontally, diagonally, antidiagonally or vertically adjacent neighbor totalling three exactly once.

4, 48, 384, 2736, 18336, 118032, 739008, 4533744, 27384288, 163381968, 965118720, 5654345136, 32898781728, 190290667152, 1095084877632, 6274151751024, 35807326610016, 203653219107408, 1154714957732736, 6529188836867376

Offset: 1

Author

R. H. Hardin, Feb 20 2016

Keywords

• nonn

Examples

			Some solutions for n=4:
..1..1. .2..3. .3..3. .1..0. .3..0. .0..2. .1..1. .2..0. .1..0. .1..1
..0..0. .2..0. .1..3. .2..0. .2..2. .2..0. .1..3. .1..0. .0..0. .0..0
..2..0. .2..0. .0..1. .0..0. .2..0. .1..0. .1..3. .0..0. .1..0. .1..0
..3..2. .2..2. .0..1. .0..0. .2..0. .0..0. .1..0. .0..0. .3..1. .1..3
		

Links

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

Crossrefs

Column 2 of A269186.

Formula

Empirical: a(n) = 10*a(n-1) - 21*a(n-2) - 20*a(n-3) - 4*a(n-4) for n>5.

Empirical g.f.: 4*x*(1 - x)^2*(1 + 2*x)^2 / (1 - 5*x - 2*x^2)^2. - Colin Barker, Jan 19 2019