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Search: id:A074875
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| A074875 |
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Numbers n such that sigma(sigma(n)-n) = phi(n). |
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+0
1
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| 2, 21, 51, 369, 3051, 3783, 5757, 6477, 6897, 7929, 15639, 15925, 20967, 33003, 50739, 58797, 73917, 75627
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OFFSET
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1,1
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EXAMPLE
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sigma(sigma(21) - 21) = sigma(32 - 21) = sigma(11) = 12 = phi(21), so 21 is a term of the sequence.
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MATHEMATICA
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Select[Range[10^5], DivisorSigma[1, DivisorSigma[1, # ] - # ] == EulerPhi[ # ] &]
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CROSSREFS
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Sequence in context: A041049 A005484 A042455 this_sequence A097718 A075681 A034520
Adjacent sequences: A074872 A074873 A074874 this_sequence A074876 A074877 A074878
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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 12 2002
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