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Search: id:A054030
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| A054030 |
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Sigma(n)/n for n such that sigma(n) is divisible by n. |
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+0
7
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| 1, 2, 2, 3, 2, 3, 2, 4, 4, 3, 4, 4, 2, 4, 4, 3, 4, 3, 2, 5, 5, 4, 3, 4, 2, 4, 4, 5, 4, 5, 5, 4, 5, 5, 4, 4, 4, 5, 4, 4, 2, 5, 4, 5, 6, 5, 5, 5, 5, 5, 5, 6, 5, 5, 4, 5, 6, 5, 4, 4, 5, 4, 5, 4, 6, 6, 6, 6, 6, 6, 6, 6, 5, 6, 6, 5, 6, 5, 6, 6, 5, 4, 4, 5, 4, 4, 5, 6, 5, 5, 4, 6, 4, 4, 6, 5, 6, 6, 6, 6, 6, 6, 6, 5, 6
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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The graph supports the conjecture that all numbers except 2 appear only a finite number of times. Sequences A000396, A005820, A027687, A046060, and A046061 give the n for which the abundancy sigma(n)/n is 2, 3, 4, 5, and 6, respectively. See A134639 for the number of n having abundancy greater than 2. - T. D. Noe, Nov 04 2007
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1600 (using Flammenkamp's data)
Eric Weisstein's World of Mathematics, Abundancy
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FORMULA
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a(n) = sigma(A007691(n))/A007691(n)
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MAPLE
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with(numtheory): for i while i < 33000 do
if sigma(i) mod i = 0 then print(sigma(i)/i) fi od;
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CROSSREFS
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Cf. A000203, A054024, A007691.
Sequence in context: A060741 A125747 A060129 this_sequence A134740 A054714 A060324
Adjacent sequences: A054027 A054028 A054029 this_sequence A054031 A054032 A054033
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KEYWORD
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nonn,easy
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AUTHOR
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Asher Auel (asher.auel(AT)reed.edu) Jan 19, 2000
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EXTENSIONS
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More terms from Jud McCranie (j.mccranie(AT)comcast.net), Jul 09 2000
More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Jun 28 2004
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