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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; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| 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
sigma () is the multiplicative sum-of-divisors function. [From Walter Nissen (nissen(AT)gtcinternet.com), Dec 16 2009]
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REFERENCES
| R. K. Guy, Unsolved Problems in Number Theory, B19.
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
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EXAMPLE
| 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
| Cf. A110751, A110819, A141718, A081377.
Cf. A000203, A110751, A110819, A141718, A081377. [From Walter Nissen (nissen(AT)gtcinternet.com), Dec 16 2009]
Sequence in context: A183019 A183016 A192853 * A183013 A055717 A090777
Adjacent sequences: A027595 A027596 A027597 * A027599 A027600 A027601
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KEYWORD
| nonn
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AUTHOR
| Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu)
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Jul 12 2008 at the suggestion of R. J. Mathar
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