A221270 Number of n X 2 arrays of occupancy after each element moves to some king-move neighbor, with every occupancy equal to zero or two.

0, 6, 16, 52, 174, 588, 1984, 6688, 22536, 75924, 255760, 861496, 2901696, 9773184, 32916280, 110861104, 373373568, 1257492096, 4235114944, 14263430416, 48037679232, 161785483872, 544874848384, 1835074738624, 6180315022560

Offset: 1

Author

R. H. Hardin, Jan 08 2013

Keywords

• nonn

Comments

Column 2 of A221273.

Examples

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

Links

• R. H. Hardin, Table of n, a(n) for n = 1..65

Crossrefs

Cf. A221273.

Formula

Empirical: a(n) = 6*a(n-1) - 10*a(n-2) + 4*a(n-3) - 2*a(n-5).

Empirical g.f.: 2*x^2*(1 - x)*(3 - 7*x + x^2) / (1 - 6*x + 10*x^2 - 4*x^3 + 2*x^5). - Colin Barker, Mar 14 2018