A250749 Number of (n+1) X (2+1) 0..2 arrays with nondecreasing x(i,j)-x(i,j-1) in the i direction and nondecreasing x(i,j)+x(i-1,j) in the j direction.

72, 237, 756, 2361, 7272, 22197, 67356, 203601, 613872, 1847757, 5555556, 16691241, 50122872, 150466917, 451597356, 1355185281, 4066342272, 12200599677, 36604944756, 109821125721, 329475960072, 988453046037, 2965409469756

Offset: 1

Author

R. H. Hardin, Nov 27 2014

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Column 2 of A250755.

Formula

Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3); a(n) = (63*3^n - 24*2^n + 3)/2.

Empirical g.f.: 3*x*(24 - 65*x + 42*x^2) / ((1 - x)*(1 - 2*x)*(1 - 3*x)). - Colin Barker, Nov 17 2018