A269053 Number of 2 X n 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two not more than once.

9, 42, 102, 360, 1068, 3288, 9864, 29472, 87312, 257184, 753504, 2197632, 6383808, 18478464, 53318784, 153414144, 440293632, 1260710400, 3602253312, 10273007616, 29245172736, 83119822848, 235886217216, 668491456512, 1892026552320

Offset: 1

Author

R. H. Hardin, Feb 18 2016

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Row 2 of A269052.

Formula

Empirical: a(n) = 4*a(n-1) - 8*a(n-3) - 4*a(n-4).

Empirical g.f.: 3*x*(3 + 2*x - 22*x^2 + 8*x^3) / (1 - 2*x - 2*x^2)^2. - Colin Barker, Jan 18 2019