A331646 - OEIS

A331646

Number of nonnegative integer matrices with 2 columns and any number of distinct nonzero rows with column sums n.

1, 3, 13, 87, 539, 2483, 14567, 81669, 402187, 2089413, 10344053, 49065413, 232941293, 1092284091, 5011510213, 22637050383, 100092546203, 439274499155, 1888145728847, 8058486875493, 33954688300771, 140741748208701, 579404121062837, 2354567807958773, 9481400353625789

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OFFSET

0,2

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..100

EXAMPLE

The a(1) = 3 matrices are:

[1 0] [0 1] [1 1]

[0 1] [1 0]

PROG

(PARI) a(n)={subst(serlaplace(polcoef(polcoef(prod(i=0, n, prod(j=0, n, 1 + x^i*y^j*z + O(x*x^n) + O(y*y^n))), n, x), n, y)/(1 + z)), z, 1)}

CROSSREFS