A269104 Number of n X 3 0..3 arrays with some element plus some horizontally or vertically adjacent neighbor totalling three no more than once.

60, 1740, 40908, 872460, 17593092, 342055548, 6482020140, 120520189980, 2208175854948, 39988864047276, 717328864510092, 12766536225007020, 225704408971133124, 3967699804321484124, 69407066832964073964

Offset: 1

Author

R. H. Hardin, Feb 19 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 3 of A269109.

Formula

Empirical: a(n) = 36*a(n-1) - 378*a(n-2) + 972*a(n-3) - 729*a(n-4) for n>5.

Empirical g.f.: 12*x*(5 - 35*x + 79*x^2 - 69*x^3 + 18*x^4) / (1 - 18*x + 27*x^2)^2. - Colin Barker, Jan 19 2019