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A074247
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Numbers n such that harmonic mean of the divisors of n is a prime.
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2
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6, 28, 140, 496, 2970, 8128, 27846, 105664, 117800, 237510, 539400, 1421280, 1539720, 2290260, 4358600, 8872200, 33550336, 50401728, 90409410, 233103780, 287425800, 318177800, 423184320, 559903400, 825120800, 1632825792, 2705020500, 3209343200, 3328809120, 4720896180
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OFFSET
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1,1
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COMMENTS
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Subsequence of A001599. Harmonic mean of divisors = n * tau(n) / sigma(n).
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LINKS
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EXAMPLE
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140*tau(140)/sigma(140) = 5, a prime, so 140 is a term of the sequence.
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MATHEMATICA
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Select[Range[10^5], PrimeQ[ # * DivisorSigma[0, # ] / DivisorSigma[1, # ]] &]
Select[Range[1600000], PrimeQ[HarmonicMean[Divisors[#]]]&] (* Harvey P. Dale, Jul 24 2019 *)
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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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