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A240975 The number of distinct prime factors of n^3-1. 1
0, 1, 2, 2, 2, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 4, 2, 2, 3, 2, 3, 3, 4, 2, 4, 3, 3, 2, 4, 3, 4, 3, 2, 3, 4, 4, 4, 2, 4, 3, 3, 3, 4, 3, 4, 4, 4, 3, 4, 2, 4, 3, 4, 2, 4, 4, 3, 4, 3, 3, 5, 2, 4, 4, 3, 3, 5, 3, 3, 3, 4, 3, 3, 4, 3, 3, 3, 3, 5, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

FORMULA

a(prime(n)) =  A245909(n).

a(n) = A001221(A068601(n)). - Michel Marcus, Aug 06 2014

EXAMPLE

3^3-1 = 26 = 2*13, so a(3)=2.

0 has no prime factors, so a(1)=0.

MAPLE

A240975 := proc(n)

    A001221(n^3-1) ;

end proc:

PROG

(Python)

from sympy import primefactors

def A240975(n):

....return len(primefactors(n**3-1)) # Chai Wah Wu, Aug 06 2014

(PARI) a(n) = if(n<=1, 0, omega(n^3-1)); \\ Joerg Arndt, Aug 06 2014

CROSSREFS

Cf. A082863, A245909, A001221.

Sequence in context: A139325 A216325 A322868 * A242166 A068211 A236832

Adjacent sequences:  A240972 A240973 A240974 * A240976 A240977 A240978

KEYWORD

nonn,easy

AUTHOR

R. J. Mathar, Aug 05 2014

STATUS

approved

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Last modified September 21 19:57 EDT 2020. Contains 337273 sequences. (Running on oeis4.)