A105972 Number of distinct prime divisors of 88...881 (with n 8's).

0, 1, 1, 2, 4, 3, 2, 2, 2, 2, 3, 3, 3, 3, 2, 2, 3, 8, 1, 3, 2, 2, 5, 2, 4, 6, 2, 2, 5, 3, 4, 4, 4, 2, 5, 5, 5, 4, 6, 3, 5, 3, 2, 5, 4, 4, 7, 4, 4, 6, 3, 5, 5, 3, 5, 6, 5, 5, 5, 4, 3, 5, 4, 2, 7, 3, 3, 8, 3, 5, 6, 7, 3, 6, 3, 3, 7, 3, 1, 5, 5, 4, 8, 4, 3, 4, 4

Offset

0,4

Links

Amiram Eldar, Table of n, a(n) for n = 0..203

Formula

a(n) = A001221(A173810(n+1)). - Michel Marcus, Jan 27 2014

Example

The number of distinct prime divisors of 81 is 1.
The number of distinct prime divisors of 881 is 1 (prime).
The number of distinct prime divisors of 8881 is 2.

Mathematica

Table[PrimeNu[(8*10^(n+1) - 71)/9], {n, 0, 50}] (* G. C. Greubel, May 16 2017 *)
PrimeNu/@Table[10 FromDigits[PadRight[{}, n, 8]]+1, {n, 0, 90}] (* Harvey P. Dale, Apr 25 2019 *)

Prog

(PARI) a(n) = omega((8*10^(n+1)-71)/9); \\ Michel Marcus, Jan 27 2014

Crossrefs

Cf. A001221, A104564, A104517, A104659, A173810.

Sequence in context: A286275 A029717 A135567 * A305024 A064134 A238847

Adjacent sequences: A105969 A105970 A105971 * A105973 A105974 A105975

Keyword

nonn,base

Author

Parthasarathy Nambi, Apr 28 2005

Extensions

More terms from Michel Marcus, Jan 27 2014

Status

approved