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Search: id:A074247
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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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+0
2
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OFFSET
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1,1
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COMMENT
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Subsequence of A001599. Harmonic mean of divisors = n * tau(n) / sigma(n).
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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, # ]] &]
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CROSSREFS
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Cf. A001599.
Sequence in context: A155588 A108051 A001599 this_sequence A053783 A110047 A163029
Adjacent sequences: A074244 A074245 A074246 this_sequence A074248 A074249 A074250
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Sep 20 2002
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