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A055734
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Number of distinct primes dividing phi(n).
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3
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0, 0, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 2, 1, 1, 1, 2, 2, 1, 2, 2, 2, 1, 2, 2, 2, 2, 2, 1, 3, 1, 2, 1, 2, 2, 2, 2, 2, 1, 2, 2, 3, 2, 2, 2, 2, 1, 3, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 3, 3, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 3, 1, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 2, 2, 3, 2, 2, 1, 2, 3, 3, 2, 2, 1, 3, 2, 2
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OFFSET
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1,7
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COMMENTS
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Murty and Murty show that the normal order of a(n) is (log log n)^2/2, that is, sum_{1 <= k <= n} a(k) ~ n/2 * (log log n)^2. - Charles R Greathouse IV, Sep 13 2013. See also Erdos-Pomerance (1985) and Erdos-Granville-et-al. (1990). - N. J. A. Sloane, Sep 02 2017
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LINKS
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FORMULA
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MATHEMATICA
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Table[PrimeNu[EulerPhi[n]], {n, 1, 50}] (* G. C. Greubel, May 08 2017 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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