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Search: id:A069931
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| A069931 |
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Number of k, 1<=k<=n, such that k divides sigma(n). |
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+0
1
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| 1, 1, 2, 1, 3, 5, 3, 3, 1, 5, 5, 4, 3, 7, 7, 1, 5, 3, 5, 6, 5, 8, 7, 10, 1, 7, 7, 7, 7, 10, 5, 5, 9, 7, 9, 3, 3, 11, 7, 10, 7, 10, 5, 11, 7, 11, 9, 4, 3, 3, 11, 5, 7, 14, 11, 14, 9, 11, 11, 14, 3, 11, 7, 1, 11, 13, 5, 1, 1, 11, 13, 11, 7, 3, 7, 5, 11, 11, 14, 9, 6, 2, 11, 11, 10, 11, 11, 15, 16
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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Sequence does not give the number of all integers dividing sigma(n) which is tau(sigma(n)) (for some n and some m>n m divides sigma(n))
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FORMULA
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Asymptotically (still conjectured) : sum(k=1, n, a(k))=C*n*ln(n)^2+o(nln(n)^2) with C=0, 35...
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PROGRAM
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(PARI) for(n=1, 150, print1(sum(i=1, n, if(sigma(n)%i, 0, 1)), ", "))
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CROSSREFS
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Adjacent sequences: A069928 A069929 A069930 this_sequence A069932 A069933 A069934
Sequence in context: A081450 A019588 A060083 this_sequence A056943 A064429 A113790
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), May 05 2002
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