A269146 Number of n X 2 0..3 arrays with some element plus some horizontally, antidiagonally or vertically adjacent neighbor totalling three exactly once.

4, 80, 768, 6224, 46464, 330192, 2270592, 15251152, 100647168, 655139152, 4217820672, 26911075152, 170416738944, 1072338720464, 6710943646848, 41800542176720, 259288295447040, 1602497927690832, 9871915467776256

Offset: 1

Author

R. H. Hardin, Feb 20 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 2 of A269152.

Formula

Empirical: a(n) = 12*a(n-1) - 38*a(n-2) + 12*a(n-3) - a(n-4) for n>5.

Empirical g.f.: 4*x*(1 - x)*(1 + 9*x - x^2 - x^3) / (1 - 6*x + x^2)^2. - Colin Barker, Jan 19 2019