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A133801 Number of distinct prime divisors of 3^n - 1. 0
1, 1, 2, 2, 2, 3, 2, 3, 3, 3, 3, 5, 2, 3, 4, 5, 3, 6, 3, 5, 4, 5, 3, 7, 4, 3, 6, 6, 4, 8, 4, 6, 5, 6, 5, 9, 3, 5, 6, 7, 4, 8, 3, 8, 8, 4, 5, 12, 7, 7, 6, 6, 4, 11, 6, 9, 7, 7, 3, 12, 3, 6, 6, 7, 6, 10, 4, 9, 6, 8, 2, 12, 5, 6, 9, 8, 7, 12, 4, 11, 9, 6, 5, 14, 6, 4, 8, 12, 4, 16, 5, 7, 7, 8, 6, 15, 4, 10, 8 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..99.

Eric Weisstein's World of Mathematics, Prime Factor.

FORMULA

a(n) = omega(3^n - 1) = A001221(3^n - 1)

EXAMPLE

a(4) = omega(3^4 - 1) = omega(80) = omega(2^4 * 5) = 2.

MATHEMATICA

Table[PrimeNu[3^n - 1], {n, 1, 50}] (* G. C. Greubel, May 21 2017 *)

PROG

(PARI) for(n = 1, 100, print1(omega(3^n - 1), ", "))

CROSSREFS

Cf. A001221, A113913.

Sequence in context: A299230 A182576 A128330 * A181630 A112310 A137734

Adjacent sequences:  A133798 A133799 A133800 * A133802 A133803 A133804

KEYWORD

nonn

AUTHOR

Ryan Propper, Jan 06 2008

STATUS

approved

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Last modified November 18 07:22 EST 2019. Contains 329252 sequences. (Running on oeis4.)