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A359895
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Number of odd-length integer partitions of n whose parts have the same mean as median.
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17
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0, 1, 1, 2, 1, 2, 3, 2, 1, 5, 5, 2, 5, 2, 8, 18, 1, 2, 19, 2, 24, 41, 20, 2, 9, 44, 31, 94, 102, 2, 125, 2, 1, 206, 68, 365, 382, 2, 98, 433, 155, 2, 716, 2, 1162, 2332, 196, 2, 17, 1108, 563, 1665, 3287, 2, 3906, 5474, 2005, 3083, 509, 2, 9029
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OFFSET
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0,4
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COMMENTS
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The length and median of such a partition are integers with product n.
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LINKS
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FORMULA
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EXAMPLE
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The a(1) = 1 through a(9) = 5 partitions:
(1) (2) (3) (4) (5) (6) (7) (8) (9)
(111) (11111) (222) (1111111) (333)
(321) (432)
(531)
(111111111)
The a(15) = 18 partitions:
(15)
(5,5,5)
(6,5,4)
(7,5,3)
(8,5,2)
(9,5,1)
(3,3,3,3,3)
(4,3,3,3,2)
(4,4,3,2,2)
(4,4,3,3,1)
(5,3,3,2,2)
(5,3,3,3,1)
(5,4,3,2,1)
(5,5,3,1,1)
(6,3,3,2,1)
(6,4,3,1,1)
(7,3,3,1,1)
(1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)
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MATHEMATICA
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Table[Length[Select[IntegerPartitions[n], OddQ[Length[#]]&&Mean[#]==Median[#]&]], {n, 0, 30}]
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PROG
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(PARI) \\ P(n, k, m) is g.f. for k parts of max size m.
P(n, k, m)={polcoef(1/prod(i=1, m, 1 - y*x^i + O(x*x^n)), k, y)}
a(n)={if(n==0, 0, sumdiv(n, d, if(d%2, my(m=n/d, h=d\2, r=n-m*(h+1)+h); polcoef(P(r, h, m)*P(r, h, r), r))))} \\ Andrew Howroyd, Jan 21 2023
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CROSSREFS
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The complement is counted by A359896.
The version for factorizations is A359910.
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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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