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Search: id:A027598
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| A027598 |
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Numbers n such that the set of prime divisors of n is equal to the set of prime divisors of sigma(n). |
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4
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| 1, 6, 28, 120, 270, 496, 672, 1080, 1638, 1782, 3780, 8128, 18600, 20580, 24948, 26208, 30240, 32640, 32760, 35640, 41850, 44226, 55860, 66960, 164640, 167400, 185220, 199584, 273000, 293760, 401310, 441936, 446880, 502740, 523776, 614250
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Multiplicities are ignored.
All even perfect numbers are in the sequence. It seems that 1 is the only odd term of the sequence. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Jul 01 2008
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REFERENCES
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R. K. Guy, Unsolved Problems in Number Theory, B19.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1000
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EXAMPLE
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273000=2^3*3*5^3*7*13 and sigma(273000)=1048320=2^8*3^2*5*7*13 so 273000 is in the sequence.
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CROSSREFS
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Cf. A110751, A110819, A141718, A081377.
Sequence in context: A027106 A089096 A026014 this_sequence A055717 A090777 A055715
Adjacent sequences: A027595 A027596 A027597 this_sequence A027599 A027600 A027601
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KEYWORD
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nonn
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AUTHOR
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Jud McCranie (j.mccranie(AT)comcast.net)
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EXTENSIONS
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Edited by njas, Jul 12 2008 at the suggestion of R. J. Mathar
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