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Search: id:A082686
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| A082686 |
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Odd nonprime integers n which have an odd number of proper divisors. |
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+0
1
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| 15, 21, 27, 33, 35, 39, 45, 51, 55, 57, 63, 65, 69, 75, 77, 85, 87, 91, 93, 95, 99, 105, 111, 115, 117, 119, 123, 125, 129, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 165, 171, 175, 177, 183, 185, 187, 189, 195, 201, 203, 205, 207, 209, 213, 215, 217, 219
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Odd nonprime numbers with even abundance and even sigma. Is their abundance always negative; i.e. are they always deficient? - Labos E. (labos(AT)ana.sote.hu), Oct 28 2003
Odd nonprime nonsquares. - Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 25 2004
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LINKS
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Author?, Unsolved Problems (see #17)
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EXAMPLE
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a(1) = 15 since 15 is the first odd nonprime number with an odd number of proper divisors.
n, #proper divisors, #divisors:
9, 2, {1, 3}
15, 3, {1, 3, 5}
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CROSSREFS
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Cf. A000396, A001065.
Sequence in context: A131651 A134642 A072974 this_sequence A102030 A026048 A047200
Adjacent sequences: A082683 A082684 A082685 this_sequence A082687 A082688 A082689
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KEYWORD
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easy,nonn
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AUTHOR
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Anne Donovan (anned3005(AT)aol.com) May 19 2003
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EXTENSIONS
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Definition corrected by Zak Seidov (zakseidov(AT)yahoo.com), Jul 21 2009
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