A280955 Number of n X 2 0..2 arrays with no element equal to more than one of its horizontal, vertical and antidiagonal neighbors and with new values introduced in order 0 sequentially upwards.

2, 9, 42, 205, 997, 4850, 23593, 114769, 558298, 2715861, 13211405, 64267362, 312630929, 1520804569, 7398009354, 35987886621, 175064388469, 851607109714, 4142673879353, 20152188344737, 98031056006074, 476875651282597

Offset: 1

Author

R. H. Hardin, Jan 11 2017

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 2 of A280961.

Formula

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

Empirical g.f.: x*(1 - x)*(1 + x)*(2 + x) / (1 - 4*x - 4*x^2 - x^3). - Colin Barker, Feb 15 2019