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A066088 Number of distinct prime factors of sigma_2(n) = A001157(n), the sum of squares of divisors of n. 2
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 (list; graph; refs; listen; history; text; internal format)
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) { for (n=1, 1000, a=omega(sigma(n, 2)); write("b066088.txt", n, " ", a) ) } \\ 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

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Last modified September 29 03:42 EDT 2020. Contains 337420 sequences. (Running on oeis4.)