

A105248


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


1



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
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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

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


CROSSREFS

Cf. A104524, A104889.
Sequence in context: A236480 A236508 A239000 * A289495 A076302 A104524
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



