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
Offset: 0
Keywords
Examples
The a(1) = 3 matrices are: [1 0] [0 1] [1 1] [0 1] [1 0]
Links
- Andrew Howroyd, Table of n, a(n) for n = 0..100
Programs
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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)}