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 A104890 Number of distinct prime divisors of 66...661 (with n 6s). 3
 1, 1, 1, 3, 2, 2, 2, 4, 1, 2, 3, 2, 3, 3, 2, 4, 1, 3, 2, 1, 1, 2, 4, 2, 3, 4, 1, 4, 4, 4, 3, 2, 4, 3, 3, 4, 3, 5, 3, 7, 2, 1, 3, 4, 3, 6, 3, 6, 4, 2, 3, 3, 6, 5, 3, 3, 5, 3, 4, 3, 5, 4, 5, 4, 1, 8, 5, 5, 2, 6, 3, 3, 3, 3, 3, 3, 2, 4, 4, 4, 7, 5, 5, 6, 3, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Also number of distinct prime factors of 6/9*(10^(n + 1) - 1) - 5. - Stefan Steinerberger, Feb 26 2006 LINKS Amiram Eldar, Table of n, a(n) for n = 1..199 FORMULA a(n) = A001221(A173805(n+1)). - Amiram Eldar, Jan 24 2020 EXAMPLE Number of distinct prime divisors of 61 is 1 (prime). Number of distinct prime divisors of 661 is 1 (prime). Number of distinct prime divisors of 6661 is 1 (prime). MATHEMATICA Table[Length[FactorInteger[6/9*(10^(n + 1) - 1) - 5]], {n, 1, 50}] (* Stefan Steinerberger, Feb 26 2006 *) Table[PrimeNu[FromDigits[PadLeft[{1}, n, 6]]], {n, 2, 90}] (* Harvey P. Dale, Jun 06 2021 *) CROSSREFS Cf. A001221, A104564, A173805. Sequence in context: A067279 A106267 A096101 * A064123 A024703 A102845 Adjacent sequences:  A104887 A104888 A104889 * A104891 A104892 A104893 KEYWORD nonn,base AUTHOR Parthasarathy Nambi, Apr 24 2005 EXTENSIONS More terms from Stefan Steinerberger, Feb 26 2006 Offset corrected and more terms added by Amiram Eldar, Jan 24 2020 STATUS approved

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Last modified January 18 01:10 EST 2022. Contains 350410 sequences. (Running on oeis4.)