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Search: id:A075867
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| A075867 |
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tau(n) = sigma(sum of prime factors of n). |
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+0
1
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| 4, 12, 18, 27, 40, 180, 250, 300, 450, 704, 780, 924, 1120, 1170, 1320, 1344, 1386, 1400, 1950, 1960, 2025, 2970, 3125, 3192, 3234, 3500, 4080, 4455, 4725, 4760, 4896, 5070, 5082, 5625, 5720, 6615, 6860, 7182, 7280, 7875, 8250, 8280, 8505, 8704
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OFFSET
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2,1
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EXAMPLE
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tau(40) = number of divisors of 40 = 8; sigma(sum of prime factors of 40) = sigma(2 + 5) = 8. Hence 40 is a term of the sequence.
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MATHEMATICA
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Select[Range[2, 10^4], DivisorSigma[1, Apply[Plus, Transpose[FactorInteger[ # ]][[1]]]] == DivisorSigma[0, # ] &]
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CROSSREFS
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Sequence in context: A074285 A057311 A063679 this_sequence A071929 A008037 A062859
Adjacent sequences: A075864 A075865 A075866 this_sequence A075868 A075869 A075870
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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), Oct 15 2002
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