

A112505


Number of primitive prime factors of 10^n1.


9



1, 1, 1, 1, 2, 2, 2, 2, 1, 1, 2, 1, 3, 1, 2, 2, 2, 2, 1, 2, 3, 3, 1, 1, 3, 2, 2, 3, 5, 3, 3, 5, 2, 3, 3, 1, 3, 1, 1, 2, 4, 3, 4, 3, 2, 4, 2, 1, 2, 3, 4, 2, 4, 2, 4, 2, 3, 2, 2, 3, 7, 1, 5, 4, 2, 2, 3, 3, 3, 2, 2, 3, 3, 3, 3, 2, 4, 4, 6, 2, 5, 2, 3, 2, 3, 3, 3, 2, 5, 3, 7, 3, 1, 3, 5, 4, 3, 2, 4, 4
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OFFSET

1,5


COMMENTS

Also the number of primes whose reciprocal is a repeating decimal of length n. The number of numbers in each row of table A046107.
By Zsigmondy's theorem, a(n) >= 1. When a(n)=1, the corresponding prime is called a unique prime (see A007498, A040017 and A051627).


LINKS



MATHEMATICA

pp={}; Table[f=Transpose[FactorInteger[10^n1]][[1]]; p=Complement[f, pp]; pp=Union[pp, p]; Length[p], {n, 66}]


CROSSREFS

Cf. A007138 (smallest primitive prime factor of 10^n1), A102347 (number of distinct prime factors of 10^n1), A046107.


KEYWORD

hard,nonn


AUTHOR



EXTENSIONS

Terms to a(276) in bfile from T. D. Noe, Jun 01 2010


STATUS

approved



