A268906 Number of 3 X n 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two exactly once.

0, 240, 1584, 9720, 54936, 299088, 1585800, 8244288, 42216696, 213602256, 1070280936, 5319700704, 26262038232, 128900271600, 629516497608, 3061019061504, 14827169463480, 71576870716944, 344483107968168

Offset: 1

Author

R. H. Hardin, Feb 15 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Row 3 of A268904.

Formula

Empirical: a(n) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4) for n>6.

Empirical g.f.: 24*x^2*(10 - 34*x + 35*x^2 - 47*x^3 + 37*x^4) / (1 - 5*x + 2*x^2)^2. - Colin Barker, Jan 16 2019