login
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
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.
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
Sequence in context: A143596 A342763 A091712 * A049798 A165198 A245526
KEYWORD
nonn
AUTHOR
Franz Vrabec, Feb 01 2007
EXTENSIONS
More terms from Michel Marcus, Aug 26 2013
STATUS
approved