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A331646
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Number of nonnegative integer matrices with 2 columns and any number of distinct nonzero rows with column sums n.
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5
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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
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0,2
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LINKS
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EXAMPLE
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The a(1) = 3 matrices are:
[1 0] [0 1] [1 1]
[0 1] [1 0]
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PROG
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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)}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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