A274798 Number of n X 3 0..2 arrays with no element equal to any value at offset (-1,-2) (-2,-1) (0,-1) or (-1,0) and new values introduced in order 0..2.

2, 8, 30, 112, 420, 1572, 5888, 22048, 82568, 309200, 1157904, 4336144, 16238112, 60808896, 227718752, 852767104, 3193464512, 11958969152, 44784259584, 167709263104, 628042022016, 2351908141824, 8807486941952, 32982506778880

Offset: 1

Author

R. H. Hardin, Jul 07 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 3 of A274803.

Formula

Empirical: a(n) = 2*a(n-1) + 6*a(n-2) + 2*a(n-3).

Empirical g.f.: 2*x*(1 + x)^2 / (1 - 2*x - 6*x^2 - 2*x^3). - Colin Barker, Jan 30 2019