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A339560
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Number of integer partitions of n that can be partitioned into distinct pairs of distinct parts, i.e., into a set of edges.
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25
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1, 0, 0, 1, 1, 2, 2, 4, 5, 8, 8, 13, 17, 22, 28, 39, 48, 62, 81, 101, 127, 167, 202, 253, 318, 395, 486, 608, 736, 906, 1113, 1353, 1637, 2011, 2409, 2922, 3510, 4227, 5060, 6089, 7242
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OFFSET
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0,6
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COMMENTS
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Naturally, such a partition must have an even number of parts. Its multiplicities form a graphical partition (A000569, A320922), and vice versa.
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LINKS
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FORMULA
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EXAMPLE
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The a(3) = 1 through a(11) = 13 partitions (A = 10):
(21) (31) (32) (42) (43) (53) (54) (64) (65)
(41) (51) (52) (62) (63) (73) (74)
(61) (71) (72) (82) (83)
(3211) (3221) (81) (91) (92)
(4211) (3321) (4321) (A1)
(4221) (5221) (4322)
(4311) (5311) (4331)
(5211) (6211) (4421)
(5321)
(5411)
(6221)
(6311)
(7211)
For example, the partition y = (4,3,3,2,1,1) can be partitioned into a set of edges in two ways:
{{1,2},{1,3},{3,4}}
{{1,3},{1,4},{2,3}},
so y is counted under a(14).
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MATHEMATICA
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strs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strs[n/d], Min@@#>d&]], {d, Select[Rest[Divisors[n]], And[SquareFreeQ[#], PrimeOmega[#]==2]&]}]];
Table[Length[Select[IntegerPartitions[n], strs[Times@@Prime/@#]!={}&]], {n, 0, 15}]
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CROSSREFS
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A339559 counts the complement in even-length partitions.
A339561 gives the Heinz numbers of these partitions.
A339619 counts factorizations of the same type.
A000070 counts non-multigraphical partitions of 2n, ranked by A339620.
A002100 counts partitions into squarefree semiprimes.
A320655 counts factorizations into semiprimes.
A320656 counts factorizations into squarefree semiprimes.
A339655 counts non-loop-graphical partitions of 2n, ranked by A339657.
A339659 counts graphical partitions of 2n into k parts.
The following count partitions of even length and give their Heinz numbers:
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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