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A060431
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Number of cubefree numbers <= n.
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7
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1, 2, 3, 4, 5, 6, 7, 7, 8, 9, 10, 11, 12, 13, 14, 14, 15, 16, 17, 18, 19, 20, 21, 21, 22, 23, 23, 24, 25, 26, 27, 27, 28, 29, 30, 31, 32, 33, 34, 34, 35, 36, 37, 38, 39, 40, 41, 41, 42, 43, 44, 45, 46, 46, 47, 47, 48, 49, 50, 51, 52, 53, 54, 54, 55, 56, 57, 58, 59, 60, 61, 61
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listen;
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OFFSET
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1,2
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REFERENCES
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I. M. Vinogradov, Elements of the Theory of Numbers,(in Russian), Moscow, 1981, p. 36.
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LINKS
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FORMULA
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a(n)=Sum_{d>=1} mu(d)*floor(n/d^3), mu(d) = Moebius function A008683.
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PROG
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(PARI) a(n)=sum(k=1, n, moebius(k)*floor(n/k^3)) \\ Benoit Cloitre, Jun 13 2007
(PARI) for (n=1, 500, a=sum(k=1, n, moebius(k)*floor(n/k^3)); write("b060431.txt", n, " ", a)) \\ Harry J. Smith, Jul 05 2009
(PARI) a(n)=my(s); forsquarefree(k=1, sqrtnint(n, 3), s+=n\k[1]^3*moebius(k)); s \\ Charles R Greathouse IV, Jan 08 2018
(Haskell)
a060431 n = a060431_list !! (n-1)
(Magma) [&+[MoebiusMu(d)*Floor(n div d^3):d in [1..n]]:n in [1..75]]; // Marius A. Burtea, Oct 02 2019
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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