A058062 - OEIS

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A058062

Number of distinct prime factors of sigma(n), the sum of the divisors of n.

8

0, 1, 1, 1, 2, 2, 1, 2, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 3, 1, 2, 2, 3, 1, 3, 2, 2, 3, 2, 1, 2, 2, 2, 2, 2, 2, 3, 2, 3, 3, 2, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 3, 2, 2, 2, 1, 3, 2, 2, 3, 2, 2, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 1, 3, 3, 2, 2, 3, 3, 3, 3, 3, 2, 3, 1, 2, 3, 3, 2, 2, 3, 2, 3, 2, 2, 4, 2

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OFFSET

1,5

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5001

FORMULA

a(n) = A001221(A000203(n)).

EXAMPLE

n=81, sigma(81) = 81+27+9+3+1 = 121 = 11^2, so a(81) = 1.

MATHEMATICA

Table[PrimeNu[DivisorSigma[1, n]], {n, 50}] (* G. C. Greubel, May 20 2017 *)

PROG

(PARI) for(n=1, 50, print1(omega(sigma(n)), ", ")) \\ G. C. Greubel, May 20 2017

CROSSREFS

Cf. A001221, A000203.

Sequence in context: A091267 A003643 A092788 * A102820 A355717 A024317

Adjacent sequences: A058059 A058060 A058061 * A058063 A058064 A058065

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 23 2000

EXTENSIONS

Offset corrected by Sean A. Irvine, Jul 22 2022

STATUS

approved