A105248 Number of distinct prime divisors of 88...887 (with n 8's).

1, 2, 1, 1, 2, 1, 3, 3, 1, 2, 3, 1, 3, 4, 4, 4, 4, 2, 3, 3, 4, 3, 2, 3, 2, 2, 3, 5, 5, 4, 3, 4, 2, 5, 6, 2, 5, 3, 2, 3, 3, 3, 3, 3, 4, 2, 4, 2, 5, 2, 3, 5, 3, 6, 4, 5, 2, 5, 4, 3, 3, 3, 4, 2, 5, 4, 4, 5, 5, 4, 5, 1, 3, 6, 4, 2, 2, 4, 3, 4, 5, 7, 6, 5, 4, 8, 4

Offset

0,2

Links

Amiram Eldar, Table of n, a(n) for n = 0..199

Formula

a(n) = A001221(A173812(n+1)). - Michel Marcus, Jan 27 2014

Example

The number of distinct prime divisors of 87 is 2.
The number of distinct prime divisors of 887 is 1 (prime).
The number of distinct prime divisors of 8887 is 1 (prime).

Mathematica

Table[PrimeNu[(8*10^(n + 1) - 17)/9], {n, 1, 50}] (* G. C. Greubel, May 21 2017 *)

Prog

(PARI) a(n) = omega((8*10^(n+1)-17)/9); \\ Michel Marcus, Jan 27 2014

Crossrefs

Cf. A104524, A104889.

Sequence in context: A236508 A364784 A239000 * A377319 A289495 A076302

Adjacent sequences: A105245 A105246 A105247 * A105249 A105250 A105251

Keyword

nonn,base

Author

Parthasarathy Nambi, Apr 29 2005

Extensions

More terms from Brian Lauer (bel136(AT)psu.edu), Feb 23 2006

Corrected and extended by Michel Marcus, Jan 27 2014

More terms from Amiram Eldar, Jan 27 2020

Status

approved