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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
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
Sequence in context: A344888 A216325 A322868 * A242166 A068211 A236832
KEYWORD
nonn,easy
AUTHOR
R. J. Mathar, Aug 05 2014
STATUS
approved

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)