A275498 Number of n X 2 0..2 arrays with no element equal to any value at offset (-2,-1) (-2,0) or (-1,-1) and new values introduced in order 0..2.

2, 9, 16, 28, 56, 104, 200, 380, 724, 1380, 2628, 5008, 9540, 18176, 34628, 65972, 125688, 239456, 456204, 869144, 1655864, 3154696, 6010220, 11450468, 21815044, 41561284, 79181152, 150853252, 287400512, 547545732, 1043165604, 1987403816

Offset: 1

Author

R. H. Hardin, Jul 30 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 2 of A275504.

Formula

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

Empirical g.f.: x*(2 + 7*x + 3*x^2 - 6*x^3 - 2*x^4 + x^5) / (1 - x - 2*x^2 + x^4). - Colin Barker, Feb 04 2019