A229795 Number of 2 X 2 0..n arrays with rows and columns in lexicographically nondecreasing order.

7, 29, 86, 205, 421, 777, 1324, 2121, 3235, 4741, 6722, 9269, 12481, 16465, 21336, 27217, 34239, 42541, 52270, 63581, 76637, 91609, 108676, 128025, 149851, 174357, 201754, 232261, 266105, 303521, 344752, 390049, 439671, 493885, 552966, 617197

Offset: 1

Author

R. H. Hardin, Sep 29 2013

Keywords

• nonn

Examples

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

Links

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

Crossrefs

Row 2 of A229794.

Formula

Empirical: a(n) = (1/3)*n^4 + (7/6)*n^3 + (13/6)*n^2 + (7/3)*n + 1.

Conjectures from Colin Barker, Sep 21 2018: (Start)

G.f.: x*(7 - 6*x + 11*x^2 - 5*x^3 + x^4) / (1 - x)^5.

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5.

(End)