A220997 Number of n X 2 arrays of occupancy after each element stays put or moves to some horizontal or vertical neighbor.

3, 31, 306, 2989, 29135, 283872, 2765627, 26943707, 262494146, 2557299561, 24914003827, 242719929760, 2364652602239, 23037176752223, 224435298485050, 2186518067974709, 21301735038155095, 207528088736659200

Offset: 1

Author

R. H. Hardin, Dec 28 2012

Keywords

• nonn

Comments

Column 2 of A221001.

Examples

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

Links

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

Crossrefs

Cf. A221001.

Formula

Empirical: a(n) = 11*a(n-1) - 11*a(n-2) - 12*a(n-3) - 2*a(n-4).

Empirical g.f.: x*(3 - 2*x - 2*x^2) / (1 - 11*x + 11*x^2 + 12*x^3 + 2*x^4). - Colin Barker, Feb 23 2018