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A102347 Number of distinct prime factors of 10^n - 1. 2
1, 2, 2, 3, 3, 5, 3, 5, 3, 5, 3, 7, 4, 5, 6, 7, 3, 8, 2, 8, 7, 7, 2, 10, 6, 7, 5, 9, 6, 13, 4, 12, 6, 7, 8, 11, 4, 4, 6, 12, 5, 14, 5, 11, 9, 7, 3, 13, 5, 11, 8, 10, 5, 12, 9, 13, 6, 9, 3, 20, 8, 6, 13, 16, 8, 14, 4, 11, 6, 13, 3, 17, 4, 8, 12, 7, 9, 15, 7, 16, 10, 8, 4, 21, 8, 9, 10, 15, 6, 21, 13 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Ray Chandler, Table of n, a(n) for n = 1..322 (first 280 terms from Max Alekseyev)

FORMULA

a(n) = A001221(A002283(n)) = A001221(10^n - 1).

a(n) = A001221(R_n) + (n^2 mod 3) = A095370(n) + (n^2 mod 3), where R_n = (10^n-1)/9 = A002275(n). That is, a(n) = A095370(n) for n=3k; otherwise a(n) = A095370(n) + 1. - Lekraj Beedassy, Jun 09 2006

MAPLE

A102347 := proc(n)

    10^n-1 ;

    A001221(%) ;

end proc: # R. J. Mathar, Dec 02 2016

MATHEMATICA

Table[PrimeNu[10^n-1], {n, 100}] (* The program will take a long time to execute *) (* Harvey P. Dale, Jan 18 2015 *)

PROG

(PARI) a(n) = omega(10^n-1); \\ Michel Marcus, Apr 22 2017

CROSSREFS

Cf. A001221, A002283, A070528.

Sequence in context: A079375 A069933 A204987 * A230846 A204908 A263027

Adjacent sequences:  A102344 A102345 A102346 * A102348 A102349 A102350

KEYWORD

nonn

AUTHOR

Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Feb 20 2005

STATUS

approved

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Last modified September 18 07:39 EDT 2020. Contains 337166 sequences. (Running on oeis4.)