A105259 Number of distinct prime divisors of 99..91 (with n 9's).

0, 2, 1, 2, 1, 3, 1, 4, 2, 3, 3, 3, 3, 4, 3, 4, 3, 6, 2, 4, 4, 3, 3, 5, 4, 7, 4, 6, 2, 6, 3, 6, 1, 2, 3, 5, 3, 10, 4, 7, 5, 4, 6, 7, 1, 7, 2, 6, 3, 5, 5, 6, 4, 6, 2, 8, 4, 7, 3, 5, 4, 11, 2, 7, 5, 8, 6, 5, 5, 7, 2, 8, 4, 7, 5, 6, 4, 6, 5, 9, 3, 9, 4, 7, 2, 9, 4

Offset

0,2

Links

Amiram Eldar, Table of n, a(n) for n = 0..229

Formula

a(n) = A001221(A170955(n+1)). - R. J. Mathar, Aug 24 2011

Example

If n=1, then the number of distinct prime divisors of 91 is 2.
If n=2, then the number of distinct prime divisors of 991 is 1 (a prime).
If n=3, then the number of distinct prime divisors of 9991 is 2.

Maple

A105259 := proc(n) local x ; x := [1, seq(9, k=1..n)] ; add(op(i, x)*10^(i-1), i=1..nops(x)) ; numtheory[factorset](%) ; nops(%) ; end proc: # R. J. Mathar, Aug 24 2011

Mathematica

Table[PrimeNu[10^(n + 1) - 9], {n, 0, 50}] (* G. C. Greubel, May 10 2017 *)

Crossrefs

Cf. A001221, A093177, A170955.

Sequence in context: A112198 A326850 A303756 * A224708 A322023 A029229

Adjacent sequences: A105256 A105257 A105258 * A105260 A105261 A105262

Keyword

nonn,base

Author

Parthasarathy Nambi, Apr 14 2005

Extensions

More terms from Amiram Eldar, Jan 24 2020

Status

approved