A104890 Number of distinct prime divisors of 66...661 (with n 6s).

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

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