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A074754
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Number of integers k such that sigma(k) divides n.
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0
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1, 1, 2, 2, 1, 3, 2, 3, 2, 1, 1, 6, 2, 3, 3, 3, 1, 5, 1, 3, 3, 1, 1, 10, 1, 2, 2, 5, 1, 5, 3, 5, 2, 1, 2, 9, 1, 2, 4, 5, 1, 8, 1, 3, 3, 1, 1, 13, 2, 1, 2, 3, 1, 7, 1, 8, 3, 1, 1, 12, 1, 4, 4, 5, 2, 3, 1, 3, 2, 3, 1, 18, 1, 2, 3, 3, 2, 6, 1, 7, 2, 1, 1, 15, 1, 1, 2, 4, 1, 10, 4, 2, 5, 1, 1, 19, 1, 5, 2, 3, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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FORMULA
| sum(k=1, n, a(k)) seems to be asymptotic to c*n*log(n) with c=0.7...
G.f.: sum(k>=1, 1/(1-x^sigma(k)))
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PROG
| (PARI) a(n)=sum(i=1, n, if(n%sigma(i), 0, 1))
(PARI) a(n)=if(n<1, 0, polcoeff(sum(k=1, n, 1/(1-x^sigma(k)), x*O(x^sigma(n))), n))
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CROSSREFS
| Sequence in context: A116608 A002947 A128180 * A030717 A071285 A008678
Adjacent sequences: A074751 A074752 A074753 * A074755 A074756 A074757
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KEYWORD
| nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Sep 28 2002
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