A095987 a(n) = gcd(n!!, (n-1)!!) where n!! = A006882.

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

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

Table of n, a(n) for n=0..37.

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

Adjacent sequences: A095984 A095985 A095986 * A095988 A095989 A095990

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