login
This site is supported by donations to The OEIS Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A122810 Number of distinct prime factors of the smallest odd number with exactly n divisors. 6
0, 1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 3, 1, 2, 2, 3, 1, 3, 1, 3, 2, 2, 1, 4, 2, 2, 3, 3, 1, 3, 1, 4, 2, 2, 2, 4, 1, 2, 2, 4, 1, 3, 1, 3, 3, 2, 1, 5, 2, 3, 2, 3, 1, 4, 2, 4, 2, 2, 1, 4, 1, 2, 3, 5, 2, 3, 1, 3, 2, 3, 1, 5, 1, 2, 3, 3, 2, 3, 1, 5, 4, 2, 1, 4, 2, 2, 2, 4, 1, 4, 2, 3, 2, 2, 2, 5, 1, 3, 3, 4, 1, 3, 1, 4, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n) = 1 iff n is prime.

LINKS

Hans Havermann, Table of n, a(n) for n = 1..2000 (using the b-file of A038547 provided by Don Reble)

FORMULA

a(n) = omega(A038547(n)), where omega(n) = A001221(n).

MATHEMATICA

PrimeNu[Table[Select[Range[1, 532000, 2], DivisorSigma[0, #] == k + 1 &, 1], {k, 0, 15}] // Flatten] (* G. C. Greubel, May 07 2017 *)

CROSSREFS

Cf. A001221, A038547, A122375.

Sequence in context: A125030 A116479 A318322 * A179953 A277013 A305822

Adjacent sequences:  A122807 A122808 A122809 * A122811 A122812 A122813

KEYWORD

nonn

AUTHOR

Ray Chandler, Sep 22 2006

EXTENSIONS

Typo in A_number fixed by Matthew Vandermast, May 03 2014

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 January 20 16:20 EST 2019. Contains 319335 sequences. (Running on oeis4.)