A105971 Number of distinct prime divisors of 66...667 (with n 6's).

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

Offset: 0

Author

Parthasarathy Nambi, Apr 28 2005

Keywords

• nonn
• base

Examples

			The number of distinct prime divisors of 67 is 1 (prime).
The number of distinct prime divisors of 667 is 2.
The number of distinct prime divisors of 6667 is 2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 0..206

Crossrefs

Cf. A001221, A067275, A104889, A104524.

Programs

Mathematica

Table[PrimeNu[(6*10^(n + 1) + 3)/9], {n, 0, 30}] (* Amiram Eldar, Jan 27 2020 *)
Table[PrimeNu[FromDigits[PadLeft[{7},n,6]]],{n,100}] (* Harvey P. Dale, Apr 05 2023 *)

Formula

a(n) = A001221(A067275(n+2)). - Amiram Eldar, Jan 27 2020