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A066815
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Number of partitions of n into sums of products.
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15
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1, 1, 2, 3, 6, 8, 14, 19, 33, 45, 69, 94, 148, 197, 289, 390, 575, 762, 1086, 1439, 2040, 2687, 3712, 4874, 6749, 8792, 11918, 15526, 20998, 27164, 36277, 46820, 62367, 80146, 105569, 135326, 177979, 227139, 296027, 377142, 490554, 622526, 804158
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OFFSET
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0,3
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COMMENTS
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Number of ways to choose a factorization of each part of an integer partition of n. - Gus Wiseman, Sep 05 2018
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LINKS
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FORMULA
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G.f.: Product_{k>=1} 1/(1-A001055(k)*x^k).
a(n) = 1/n*Sum_{k=1..n} a(n-k)*b(k), n > 0, a(0)=1, b(k)=Sum_{d|k} d*(A001055(d))^(k/d).
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EXAMPLE
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The a(6) = 14 partitions of 6 into sums of products:
6, 2*3,
5+1, 4+2, 2*2+2, 3+3,
4+1+1, 2*2+1+1, 3+2+1, 2+2+2,
3+1+1+1, 2+2+1+1,
2+1+1+1+1,
1+1+1+1+1+1.
(End)
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MATHEMATICA
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facs[n_]:=If[n<=1, {{}}, Join@@Table[(Prepend[#1, d]&)/@Select[facs[n/d], Min@@#1>=d&], {d, Rest[Divisors[n]]}]];
Table[Length[Join@@Table[Tuples[facs/@ptn], {ptn, IntegerPartitions[n]}]], {n, 20}] (* Gus Wiseman, Sep 05 2018 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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