login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A095987 a(n) = gcd(n!!, (n-1)!!) where n!! = A006882. 1
1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 15, 15, 45, 45, 315, 315, 315, 315, 2835, 2835, 14175, 14175, 155925, 155925, 467775, 467775, 6081075, 6081075, 42567525, 42567525, 638512875, 638512875, 638512875, 638512875, 10854718875, 10854718875, 97692469875, 97692469875 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,7
COMMENTS
Let f_n(m) be a multifactorial: for m = positive integer, f_n(m) = Product_{k=0..floor((m-1)/n)} (m - k*n). E.g., f_2(m) = m!!. f_n(0) is defined as 1.
a(2m) = a(2m+1) = the largest odd divisor of m! (which is A049606).
LINKS
MAPLE
a:= n-> (d-> gcd(d(n), d(n-1)))(doublefactorial):
seq(a(n), n=0..40); # Alois P. Heinz, Oct 26 2019
MATHEMATICA
f[n_] := GCD[n!!, (n - 1)!! ]; Table[ f[n], {n, 35}]
GCD@@#&/@Partition[Range[0, 40]!!, 2, 1] (* Harvey P. Dale, May 04 2015 *)
CROSSREFS
a(2n) gives A049606.
Sequence in context: A287505 A288124 A286865 * A278667 A232984 A098535
KEYWORD
nonn
AUTHOR
Leroy Quet, Jul 18 2004
EXTENSIONS
Edited and extended by Robert G. Wilson v, Jul 19 2004
Missing a(0)=1 inserted by Alois P. Heinz, Oct 26 2019
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 19 03:33 EDT 2024. Contains 370952 sequences. (Running on oeis4.)