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A105972 Number of distinct prime divisors of 88...881 (with n 8's). 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 22 03:20 EDT 2021. Contains 347605 sequences. (Running on oeis4.)