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Search: id:A067382
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| A067382 |
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Numbers n such that sigma(phi(n))/sigma(n) = 2. |
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+0
6
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| 13, 71, 89, 203, 305, 319, 667, 1363, 1421, 1525, 1711, 1889, 2407, 2933, 3103, 4609, 4615, 4843, 5191, 6583, 7123, 7625, 7627, 9947, 10063, 10411, 11107, 13543, 13891, 14587, 16327, 17023, 19693, 20851, 23075, 24331, 24721, 25027, 25723
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Sequence is infinite. Contains subsequences like 5^i*61, 5^i*13*71, 7^i*29 ... (See also Farideh Firoozbakht's comment on A033631.) - vim(AT)gmx.li, Nov 03 2006
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MATHEMATICA
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For[ n=1, True, n++, If[ DivisorSigma[ 1, EulerPhi[ n ] ]/DivisorSigma[ 1, n ]==2, Print[ n ] ] ]
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CROSSREFS
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Cf. A033631, A066831, A067383, A067384, A067385.
Sequence in context: A050403 A031442 A066831 this_sequence A158941 A128003 A060103
Adjacent sequences: A067379 A067380 A067381 this_sequence A067383 A067384 A067385
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KEYWORD
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nonn
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AUTHOR
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Dean Hickerson (dean.hickerson(AT)yahoo.com), Jan 20 2002
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