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Search: id:A068390
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| A068390 |
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Numbers n such that sigma(n)=4*phi(n). |
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+0
14
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| 14, 105, 248, 418, 1485, 3135, 3596, 3956, 4064, 5396, 8636, 20026, 23374, 25714, 35074, 35343, 39105, 41656, 55154, 56134, 56536, 71145, 74613, 87087, 124605, 150195, 175305, 192855, 263055
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If 2^p-1 is prime (a Mersenne prime) then 2^(p-2)*(2^p-1) is in the sequence. So 2^(A000043-2)*(2^A000043-1) is a subsequence of this sequence. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Feb 23 2005
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REFERENCES
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D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, p. 88.
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PROGRAM
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PARI : for(n=1, 300000, if(sigma(n)==4*eulerphi(n), print1(n, ", ")))
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CROSSREFS
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Cf. A000010, A000203, A079546.
Cf. A000043.
Sequence in context: A089508 A131709 A139614 this_sequence A008506 A010966 A022579
Adjacent sequences: A068387 A068388 A068389 this_sequence A068391 A068392 A068393
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 03 2002
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