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
Examples
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.
Links
- Amiram Eldar, Table of n, a(n) for n = 0..203
Programs
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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 *) -
PARI
a(n) = omega((8*10^(n+1)-71)/9); \\ Michel Marcus, Jan 27 2014
Formula
Extensions
More terms from Michel Marcus, Jan 27 2014