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

Author

Parthasarathy Nambi, Apr 24 2005

Keywords

• nonn
• base

Comments

Also number of distinct prime factors of 6/9*(10^(n + 1) - 1) - 5. - Stefan Steinerberger, Feb 26 2006

Examples

			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).
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..199

Crossrefs

Cf. A001221, A104564, A173805.

Programs

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 *)

Formula

a(n) = A001221(A173805(n+1)). - Amiram Eldar, Jan 24 2020

Extensions

More terms from Stefan Steinerberger, Feb 26 2006

Offset corrected and more terms added by Amiram Eldar, Jan 24 2020