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A078120 Number of distinct prime divisors of n-th balanced number. 1
0, 1, 1, 2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 3, 3, 3, 3, 4, 2, 3, 3, 3, 3, 4, 4, 3, 3, 4, 4, 3, 3, 4, 4, 3, 3, 4, 3, 3, 4, 4, 3, 3, 4, 4, 5, 4, 4, 4, 3, 3, 4, 4, 3, 2, 4, 4, 4, 4, 3, 4, 3, 4, 4, 5, 4, 4, 4, 3, 4, 3, 4, 4, 5, 4, 4, 4, 4, 4, 4, 5, 3, 4, 5, 4, 5, 5, 4, 5, 4, 4, 4, 5, 4, 4, 5, 4, 4, 3, 5, 5, 4, 4, 5, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
FORMULA
a(n) = A001221(A020492(n)).
EXAMPLE
The 575th balanced number is 2089542 = 2*3*7*13*43*89, so a(575)=6; sigma(2089542)/phi(2089542) = 10.
MATHEMATICA
PrimeNu /@ Select[Range[10^5], Divisible[DivisorSigma[1, #], EulerPhi[#]] &] (* Amiram Eldar, Dec 05 2019 *)
CROSSREFS
Sequence in context: A163374 A108502 A260235 * A057525 A331362 A139325
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 06 2002
STATUS
approved

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Last modified March 5 05:10 EST 2024. Contains 370537 sequences. (Running on oeis4.)