A105255 Number of distinct prime divisors of 88...889 (with n 8's).
1, 1, 2, 2, 2, 2, 2, 2, 5, 3, 2, 5, 3, 1, 6, 4, 1, 4, 4, 3, 4, 4, 2, 3, 3, 3, 4, 4, 2, 6, 5, 4, 6, 3, 1, 5, 6, 2, 6, 4, 3, 7, 5, 2, 8, 7, 4, 7, 5, 4, 7, 3, 7, 5, 3, 3, 9, 6, 5, 3, 3, 3, 7, 3, 4, 6, 4, 2, 6, 7, 5, 7, 7, 4, 7, 6, 4, 5, 3, 4, 6, 2, 2, 7, 5, 3, 9, 6, 4, 8, 6, 7, 5, 2, 5, 6, 5, 5, 7, 7
Offset: 0
Examples
The number of distinct prime divisors of 89 is 1 (prime). The number of distinct prime divisors of 889 is 2. The number of distinct prime divisors of 8889 is 2.
Links
- Amiram Eldar, Table of n, a(n) for n = 0..225
Crossrefs
Cf. A104543.
Programs
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Mathematica
Table[PrimeNu[(8*10^(n + 1) + 1)/9], {n, 0,50}] (* G. C. Greubel, May 16 2017 *) -
PARI
a(n) = omega((8*10^(n+1)+1)/9); \\ Michel Marcus, Jan 27 2014