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A362801
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Numbers whose set of divisors can be partitioned into disjoint parts, all of length > 1 and having integer harmonic mean.
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2
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6, 12, 18, 24, 28, 30, 40, 42, 45, 48, 54, 56, 60, 66, 72, 78, 84, 90, 96, 102, 108, 112, 114, 120, 126, 132, 135, 138, 140, 144, 150, 156, 162, 168, 174, 180, 186, 192, 196, 198, 200, 204, 210, 216, 220, 222, 224, 225, 228, 234, 240, 246, 252, 258, 264, 270, 276
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OFFSET
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1,1
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COMMENTS
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Numbers k such that A362802(k) > 0.
Includes all the harmonic numbers (A001599) except for 1, since the set of their divisors has an integer harmonic mean (in this case the partition is into a single part).
This sequence is infinite. For example, if k is a term and p is a prime that does not divide k, then k*p is also a term.
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LINKS
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EXAMPLE
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12 is a term since its set of divisors, {1, 2, 3, 4, 6, 12} can be partitioned into 2 disjoint parts, {1, 2, 3, 6} and {4, 12}, whose harmonic means, 2 and 6, are both integers.
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MATHEMATICA
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harmQ[s_] := AllTrue[s, Length[#] > 1 && IntegerQ[HarmonicMean[#]] &]; q[n_] := Module[{d = Divisors[n], r}, r = ResourceFunction["SetPartitions"][d]; AnyTrue[r, harmQ]]; Do[If[q[n], Print[n]], {n, 1, 100}]
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CROSSREFS
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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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