A066088 Number of distinct prime factors of sigma_2(n), where sigma_2(n) = A001157(n).

0, 1, 2, 2, 2, 2, 2, 2, 2, 3, 2, 4, 3, 2, 3, 2, 3, 3, 2, 4, 2, 3, 3, 3, 3, 3, 3, 4, 2, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 4, 2, 2, 3, 4, 3, 3, 4, 4, 3, 4, 3, 5, 3, 3, 3, 3, 3, 3, 2, 5, 2, 4, 4, 2, 4, 3, 3, 5, 3, 3, 2, 4, 4, 3, 5, 4, 3, 3, 2, 4, 2, 3, 4, 4, 4, 3, 3, 4, 3, 4, 3, 5, 4, 4, 3, 5, 3, 4, 4, 3, 2, 3, 3, 3, 3

Offset

1,3

Links

Harry J. Smith, Table of n, a(n) for n=1..1000

Formula

a(n) = A001221(A001157(n)).

Example

sigma_2(12) = 144 + 36 + 16 + 9 + 4 + 1 = 210, so a(12)=4.

Mathematica

PrimeNu[DivisorSigma[2, Range[110]]] (* Harvey P. Dale, Feb 23 2015 *)

Prog

(PARI) a(n) = { omega(sigma(n, 2)) } \\ Harry J. Smith, Nov 11 2009

Crossrefs

Cf. A001157, A001221.

Sequence in context: A278950 A029411 A165093 * A139326 A029243 A306240

Adjacent sequences: A066085 A066086 A066087 * A066089 A066090 A066091

Keyword

nonn

Author

Labos Elemer, Dec 04 2001

Extensions

Offset changed from 0 to 1 by Harry J. Smith, Nov 11 2009

Status

approved