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Search: id:A069928
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| A069928 |
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Number of k, 1<=k<=n, such that tau(k) divides sigma(k) where tau(x) is the number of divisors of x and sigma(x) the sum of divisors of x. |
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+0
1
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| 1, 1, 2, 2, 3, 4, 5, 5, 5, 5, 6, 6, 7, 8, 9, 9, 10, 10, 11, 12, 13, 14, 15, 15, 15, 15, 16, 16, 17, 18, 19, 19, 20, 20, 21, 21, 22, 23, 24, 24, 25, 26, 27, 28, 29, 30, 31, 31, 32, 32, 33, 33, 34, 35, 36, 37, 38, 38, 39, 40, 41, 42, 42, 42, 43, 44, 45, 46, 47, 48, 49, 49, 50, 50
(list; graph; listen)
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OFFSET
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1,3
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FORMULA
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a(n)=Card(k: 1<=k<=n : sigma(k) == 0 (mod tau(k) ) : lim n -> infinity a(n)/n=C=0, 8...
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PROGRAM
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(PARI) for(n=1, 150, print1(sum(i=1, n, if(sigma(i)%numdiv(i), 0, 1)), ", "))
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CROSSREFS
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Sequence in context: A030564 A094457 A022820 this_sequence A135585 A081094 A054633
Adjacent sequences: A069925 A069926 A069927 this_sequence A069929 A069930 A069931
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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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