A217268 Number of n X 3 arrays of occupancy after each element moves to some horizontal or vertical neighbor.

2, 64, 1472, 33856, 772800, 17640000, 402494400, 9183772224, 209543184576, 4781079618624, 109088244863424, 2489028863068224, 56791310102324928, 1295787666826276416, 29565538631067860928, 674586660240498844224

Offset: 1

Author

R. H. Hardin, Sep 29 2012

Keywords

• nonn

Comments

Column 3 of A217273.

Examples

			Some solutions for n=3:
..1..1..0....1..1..0....1..3..1....1..1..2....0..2..2....0..1..0....1..2..0
..2..0..1....0..1..1....1..0..0....2..0..0....0..0..0....1..2..3....1..1..1
..1..1..2....1..3..1....0..1..2....1..2..0....1..3..1....2..0..0....1..1..1
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..28

Crossrefs

Cf. A217273.

Formula

Empirical: a(n) = 24*a(n-1) - 648*a(n-3) + 729*a(n-4) for n>5.

Empirical g.f.: 2*x*(1 + 8*x - 32*x^2 - 88*x^3 + 135*x^4) / ((1 - 24*x + 27*x^2)*(1 - 27*x^2)). - Colin Barker, Jul 23 2018