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A261447 The number of distinct prime factors of the number of proper divisors of n. 1
0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,63
COMMENTS
Starts to differ from A174889 at n=64.
The first 2 occurs at n = 64, the first 3 at n = 1081080.
The first 4 occurs at n = 75424789440 and the first 5 occurs at 2474044411193114760000. - Charles R Greathouse IV, Aug 20 2015
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 2..10000
FORMULA
a(n) = A001221(A032741(n)).
MAPLE
A261447 := proc(n)
end proc:
MATHEMATICA
PrimeNu[DivisorSigma[0, #]-1&/@Range[2, 82]] (* Ivan N. Ianakiev, Aug 20 2015 *)
PROG
(PARI) a(n)=omega(numdiv(n)-1) \\ Charles R Greathouse IV, Aug 20 2015
CROSSREFS
Sequence in context: A144411 A138253 A341969 * A287325 A336387 A358217
KEYWORD
nonn
AUTHOR
R. J. Mathar, Aug 19 2015
STATUS
approved

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Last modified March 28 16:58 EDT 2024. Contains 371254 sequences. (Running on oeis4.)