A269284 Number of n X 3 0..3 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling three no more than once.

60, 2124, 62748, 1698732, 43674876, 1085203980, 26317946844, 626778812268, 14718495557052, 341767357185996, 7863372461151900, 179542238849355564, 4073026776304945788, 91888997272241919372, 2063133077083679521116

Offset: 1

Author

R. H. Hardin, Feb 21 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 3 of A269289.

Formula

Empirical: a(n) = 42*a(n-1) - 441*a(n-2).

Conjectures from Colin Barker, Jan 21 2019: (Start)

G.f.: 12*x*(5 - 33*x) / (1 - 21*x)^2.

a(n) = 4 * 3^n * 7^(n-2) * (24*n+11).

(End)