A104889 Number of distinct prime divisors of 44...447 (with n 4s).

1, 2, 1, 2, 3, 2, 2, 4, 1, 3, 2, 3, 2, 2, 2, 2, 3, 3, 1, 5, 4, 4, 4, 7, 1, 4, 2, 5, 3, 3, 3, 3, 3, 6, 4, 5, 3, 2, 3, 5, 6, 7, 4, 4, 4, 2, 5, 3, 3, 6, 4, 6, 2, 5, 3, 5, 3, 6, 4, 6, 4, 6, 3, 5, 6, 6, 4, 5, 2, 4, 7, 7, 3, 5, 3, 3, 3, 5, 4, 10, 5, 4, 3, 5, 3, 2, 4

Offset: 1

Author

Parthasarathy Nambi, Apr 24 2005

Keywords

• nonn

Comments

Also number of distinct prime factors of (10^(n + 1) - 1)*4/9 + 3. - Stefan Steinerberger, Feb 21 2006

Examples

			Number of distinct prime divisors of 47 is 1 (prime).
Number of distinct prime divisors of 447 is 2.
Number of distinct prime divisors of 4447 is 1 (prime).
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..201

Crossrefs

Cf. A001221, A104564, A173772.

Programs

Mathematica

Table[Length[FactorInteger[(10^(n + 1) - 1)*4/9 + 3]], {n, 1, 40}] (* Stefan Steinerberger, Feb 21 2006 *)

Formula

a(n) = A001221(A173772(n+1)). - Amiram Eldar, Jan 27 2020

Extensions

More terms from Stefan Steinerberger, Feb 21 2006

Offset corrected and more terms added by Amiram Eldar, Jan 27 2020