|
|
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
|
|
|
FORMULA
|
|
|
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
|
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|