login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Amiram Eldar, Table of n, a(n) for n = 1..10000

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

Cf. A020492, A001221.

Sequence in context: A163374 A108502 A260235 * A057525 A331362 A139325

Adjacent sequences:  A078117 A078118 A078119 * A078121 A078122 A078123

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 06 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 27 10:31 EDT 2021. Contains 346304 sequences. (Running on oeis4.)