A269103 Number of n X 2 0..3 arrays with some element plus some horizontally or vertically adjacent neighbor totalling three no more than once.

16, 180, 1740, 15540, 132300, 1090740, 8787660, 69580980, 543538380, 4200069300, 32167589580, 244542858420, 1847388128460, 13880833735860, 103809654007500, 773174303047860, 5737767196302540, 42443199898890420, 313054205965641420

Offset: 1

Author

R. H. Hardin, Feb 19 2016

Keywords

• nonn

Comments

Column 2 of A269109.

Examples

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

Links

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

Crossrefs

Cf. A269109.

Formula

Empirical: a(n) = 14*a(n-1) - 49*a(n-2) for n>3.

Conjectures from Colin Barker, Mar 21 2018: (Start)

G.f.: 4*x*(4 - 11*x + x^2) / (1 - 7*x)^2.

a(n) = 60*7^(n-3)*(8*n+5) for n>1.

(End)