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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A137484 Numbers with 21 divisors. 6
576, 1600, 2916, 3136, 7744, 10816, 18225, 18496, 23104, 33856, 35721, 53824, 61504, 62500, 87616, 88209, 107584, 118336, 123201, 140625, 141376, 179776, 210681, 222784, 238144, 263169, 287296, 322624, 341056, 385641, 399424, 440896 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Maple implementation: see A030513.

Numbers of the form p^20 or p^2*q^6 (A189990) where p and q are distinct primes. - R. J. Mathar, Mar 01 2010

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

FORMULA

A000005(a(n))=21.

MATHEMATICA

Select[Range[450000], DivisorSigma[0, #]==21&] (* Vladimir Joseph Stephan Orlovsky, May 03 2011 *)

PROG

(PARI) is(n)=numdiv(n)==21 \\ Charles R Greathouse IV, Jun 19 2016

CROSSREFS

Cf. A030513-A030516, A030626, A030627, A030634-A030638, A005179, A003680, A096932, A061286, A061283.

Sequence in context: A235181 A268773 A250789 * A189990 A064254 A281242

Adjacent sequences:  A137481 A137482 A137483 * A137485 A137486 A137487

KEYWORD

nonn

AUTHOR

R. J. Mathar, Apr 22 2008

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified September 26 05:09 EDT 2017. Contains 292502 sequences.