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A343661
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Sum of numbers of y-multisets of divisors of x for each x >= 1, y >= 0, x + y = n.
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4
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1, 2, 4, 7, 12, 19, 30, 46, 70, 105, 155, 223, 316, 443, 619, 865, 1210, 1690, 2354, 3263, 4497, 6157, 8368, 11280, 15078, 19989, 26296, 34356, 44626, 57693, 74321, 95503, 122535, 157101, 201377, 258155, 330994, 424398, 544035, 696995, 892104, 1140298, 1455080
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = Sum_{k=1..n} binomial(sigma(k) + n - k - 1, n - k).
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EXAMPLE
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The a(5) = 12 multisets of divisors:
{1,1,1,1} {1,1,1} {1,1} {1} {}
{1,1,2} {1,3} {2}
{1,2,2} {3,3} {4}
{2,2,2}
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MATHEMATICA
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multchoo[n_, k_]:=Binomial[n+k-1, k];
Table[Sum[multchoo[DivisorSigma[0, k], n-k], {k, n}], {n, 10}]
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CROSSREFS
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Antidiagonal sums of the array A343658 (or row sums of the triangle).
A007318 counts k-sets of elements of {1..n}.
A059481 counts k-multisets of elements of {1..n}.
Cf. A000169, A000312, A009998, A062319, A067824, A143773, A146291, A176029, A184389, A285572, A326077, A327527, A334996, A343652, A343657.
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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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