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A104564
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Number of distinct prime divisors of 77...771 (with n 7's).
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6
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1, 2, 2, 2, 3, 2, 2, 2, 2, 3, 3, 1, 3, 4, 2, 2, 3, 2, 1, 4, 3, 1, 3, 3, 2, 3, 4, 2, 7, 1, 5, 6, 3, 3, 4, 3, 4, 5, 5, 3, 5, 4, 2, 3, 3, 6, 2, 2, 6, 5, 4, 3, 4, 4, 6, 2, 6, 5, 4, 4, 4, 5, 3, 3, 5, 2, 6, 3, 5, 5, 4, 6, 4, 6, 5, 3, 3, 4, 4, 4, 4, 6, 4, 3, 6, 5, 3
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OFFSET
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1,2
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COMMENTS
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Also number of distinct prime factors of (10^(n + 1) - 1)*7/9 - 6. - Stefan Steinerberger, Mar 01 2006
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LINKS
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FORMULA
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EXAMPLE
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The number of distinct prime divisors of 71 is 1 (prime).
The number of distinct prime divisors of 771 is 2.
The number of distinct prime divisors of 7771 is 2.
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MATHEMATICA
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Table[Length[FactorInteger[(10^(n + 1) - 1)*7/9 - 6]], {n, 1, 50}] (* Stefan Steinerberger, Mar 01 2006 *)
PrimeNu/@(FromDigits/@Table[PadLeft[{1}, n, 7], {n, 2, 55}]) (* Harvey P. Dale, Apr 22 2011 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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Offset corrected and more terms added by Amiram Eldar, Jan 24 2020
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STATUS
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approved
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