

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
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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



