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Search: id:A020493
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| A020493 |
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Numbers n such that d(n) (number of divisors) divides phi(n) (Euler function) divides sigma(n) (sum of divisors). |
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+0
2
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| 1, 3, 15, 30, 35, 56, 70, 78, 105, 140, 168, 190, 210, 248, 264, 357, 420, 570, 616, 630, 714, 744, 812, 840, 910, 1045, 1240, 1485, 1672, 1848, 2090, 2214, 2436, 2580, 2730, 3080, 3135, 3339, 3596, 3720, 3956, 4064, 4180, 4522, 4674, 5016, 5049, 5278, 5396
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Numbers n such that sigma_0(n) divides phi(n) divides sigma_1(n).
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REFERENCES
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D. Wells, Curious and interesting numbers, Penguin Books, p. 130
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EXAMPLE
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210 has 16 divisors, which divides phi(210)=48, which in turn divides sigma(210)=576, so 210 is a member of the sequence.
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CROSSREFS
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Cf. A000005, A000010, A000203.
Sequence in context: A147344 A053519 A039666 this_sequence A087183 A106354 A018972
Adjacent sequences: A020490 A020491 A020492 this_sequence A020494 A020495 A020496
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KEYWORD
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nonn
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AUTHOR
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David W. Wilson (davidwwilson(AT)comcast.net)
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EXTENSIONS
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Wells incorrectly has 52 instead of 56.
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