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A061260
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G.f.: Product_{k>=1} (1-y*x^k)^(-numbpart(k)), where numbpart(k) = number of partitions of k, cf. A000041.
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18
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1, 2, 1, 3, 2, 1, 5, 6, 2, 1, 7, 11, 6, 2, 1, 11, 23, 15, 6, 2, 1, 15, 40, 32, 15, 6, 2, 1, 22, 73, 67, 37, 15, 6, 2, 1, 30, 120, 134, 79, 37, 15, 6, 2, 1, 42, 202, 255, 172, 85, 37, 15, 6, 2, 1, 56, 320, 470, 348, 187, 85, 37, 15, 6, 2, 1, 77, 511, 848, 697, 397, 194, 85, 37, 15, 6, 2, 1
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OFFSET
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1,2
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COMMENTS
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Number of orderless twice-partitions of n of length k. A twice-partition of n is a choice of a partition of each part in a partition of n. The T(5,3) = 6 orderless twice-partitions: (3)(1)(1), (21)(1)(1), (111)(1)(1), (2)(2)(1), (2)(11)(1), (11)(11)(1). - Gus Wiseman, Mar 23 2018
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LINKS
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EXAMPLE
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: 1;
: 2, 1;
: 3, 2, 1;
: 5, 6, 2, 1;
: 7, 11, 6, 2, 1;
: 11, 23, 15, 6, 2, 1;
: 15, 40, 32, 15, 6, 2, 1;
: 22, 73, 67, 37, 15, 6, 2, 1;
: 30, 120, 134, 79, 37, 15, 6, 2, 1;
: 42, 202, 255, 172, 85, 37, 15, 6, 2, 1;
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MAPLE
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b:= proc(n, i, p) option remember; `if`(p>n, 0, `if`(n=0, 1,
`if`(min(i, p)<1, 0, add(b(n-i*j, i-1, p-j)*binomial(
combinat[numbpart](i)+j-1, j), j=0..min(n/i, p)))))
end:
T:= (n, k)-> b(n$2, k):
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MATHEMATICA
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b[n_, i_, p_] := b[n, i, p] = If[p > n, 0, If[n == 0, 1, If[Min[i, p] < 1, 0, Sum[b[n - i*j, i - 1, p - j]*Binomial[PartitionsP[i] + j - 1, j], {j, 0, Min[n/i, p]}]]]];
T[n_, k_] := b[n, n, k];
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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