A185561 1/4 the number of n X 3 0..3 arrays with no element equal both to the element above and to the element to its left.

16, 900, 50580, 2842560, 159749820, 8977824540, 504547256880, 28355191537860, 1593541291098420, 89555869973406240, 5032975230384726780, 282849573983126145660, 15895941831670877597520, 893340453575999346503940

Offset: 1

Author

R. H. Hardin, Jan 31 2011

Keywords

• nonn

Comments

Column 3 of A185567.

Examples

			Some solutions for 5 X 3 with a(1,1)=0:
..0..0..0....0..0..0....0..0..0....0..0..0....0..0..0....0..0..0....0..0..0
..0..2..2....0..2..0....0..2..0....0..2..2....0..2..0....0..2..0....0..2..0
..2..0..1....0..1..3....0..2..1....0..3..2....0..1..0....0..3..2....0..2..3
..0..1..3....2..2..2....1..2..2....3..0..3....3..2..3....0..3..3....0..2..3
..3..3..0....1..2..0....3..3..3....0..3..1....0..1..0....3..1..0....1..1..3
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A185567.

Formula

Empirical: a(n) = 57*a(n-1) - 45*a(n-2).

Empirical g.f.: 4*x*(4 - 3*x) / (1 - 57*x + 45*x^2). - Colin Barker, Apr 16 2018