A252870 Number of n X 2 nonnegative integer arrays with upper left 0 and lower right n+2-4 and value increasing by 0 or 1 with every step right or down.

0, 1, 8, 26, 61, 120, 211, 343, 526, 771, 1090, 1496, 2003, 2626, 3381, 4285, 5356, 6613, 8076, 9766, 11705, 13916, 16423, 19251, 22426, 25975, 29926, 34308, 39151, 44486, 50345, 56761, 63768, 71401, 79696, 88690, 98421, 108928, 120251, 132431, 145510

Offset: 1

Author

R. H. Hardin, Dec 24 2014

Keywords

• nonn

Comments

Column 2 of A252876.

Examples

			All solutions for n=3:
..0..0....0..0....0..0....0..1....0..1....0..0....0..1....0..0
..0..0....0..0....0..1....1..1....0..1....0..1....0..1....1..1
..0..1....1..1....1..1....1..1....1..1....0..1....0..1....1..1
		

Links

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

Formula

Empirical: a(n) = (1/24)*n^4 + (5/12)*n^3 - (13/24)*n^2 - (11/12)*n + 1.

Empirical: G.f.: -x^2*(1+3*x-4*x^2+x^3) / (x-1)^5. - R. J. Mathar, Nov 21 2015