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!)
A125721 a(n)=2*n!/d(n!); d(m)=A000005(m) is the number of divisors of m. 0
2, 2, 2, 3, 6, 15, 48, 168, 840, 4536, 26880, 147840, 1209600, 7862400, 67267200, 648648000, 7783776000, 66162096000, 871782912000, 8281937664000, 118562476032000, 1680623097753600, 23416681828700160, 269291841030051840, 5109094217170944000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(3)=3 and a(5)=15 are the only odd numbers in this sequence.

REFERENCES

P. Erdos, solved by J. Fiedler, Elem. Math. 16 (1961), 42-44, Aufgabe 374.

LINKS

Table of n, a(n) for n=0..24.

FORMULA

a(n)=2*A000142(n)/A027423(n).

EXAMPLE

a(4)=2*4!/d(4!)=2*24/8=6.

MATHEMATICA

Table[(2n!)/DivisorSigma[0, n!], {n, 0, 25}] (* Harvey P. Dale, Jun 01 2014 *)

PROG

(PARI) a(n) = 2*n!/numdiv(n!); \\ Michel Marcus, Aug 26 2013

CROSSREFS

Cf. A000142, A027423.

Sequence in context: A218694 A143596 A091712 * A049798 A165198 A245526

Adjacent sequences:  A125718 A125719 A125720 * A125722 A125723 A125724

KEYWORD

nonn

AUTHOR

Franz Vrabec, Feb 01 2007

EXTENSIONS

More terms from Michel Marcus, Aug 26 2013

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 August 7 17:44 EDT 2020. Contains 336278 sequences. (Running on oeis4.)