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Search: id:A067651
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| A067651 |
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Numbers n such that sigma(n) = phi(prime(n)-1). |
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+0
3
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| 1, 7, 19, 47, 115, 177, 280, 297, 340, 406, 470, 930, 1240, 1608, 1836, 2232, 2380, 2484, 4326, 8360, 33864, 166152, 216216, 220248, 299250, 394500
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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No further term below 4*10^6.
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EXAMPLE
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sigma(19) = 20, prime(19) = 67, phi(66) = 20, hence 20 is a term.
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PROGRAM
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(PARI) m=400000; for(n=1, m, if(sigma(n)==eulerphi(prime(n)-1), print1(n, ", ")))
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CROSSREFS
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Cf. A107815, A107816.
Adjacent sequences: A067648 A067649 A067650 this_sequence A067652 A067653 A067654
Sequence in context: A139865 A000491 A097039 this_sequence A090025 A003232 A018728
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KEYWORD
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nonn,more
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 23 2002
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EXTENSIONS
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More terms from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Mar 02 2002, revised May 24 2005
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