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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
OFFSET
1,3
LINKS
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
Sequence in context: A278950 A029411 A165093 * A139326 A029243 A306240
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 04 2001
EXTENSIONS
OFFSET changed from 0 to 1 by Harry J. Smith, Nov 11 2009
STATUS
approved