A232618 a(n) = (2n)!! mod (2n-1)!! where k!! = A006882(k).

0, 2, 3, 69, 60, 4500, 104580, 186795, 13497435, 442245825, 13003053525, 64585694250, 3576632909850, 147580842959550, 5708173568847750, 27904470362393625, 2292043480058957625, 126842184377462428875, 6371504674680470700375, 312265748715684068930625

Offset

1,2

Comments

(2n)!! is the product of first n even numbers, (2n-1)!! is the product of first n odd numbers.

Links

Table of n, a(n) for n=1..20.

Formula

a(n) = A006882(2*n) mod A006882(2*n-1).

Example

a(3) = A006882(6) mod A006882(5) = 2*4*6 mod 1*3*5 = 48 mod 15 = 3.

Mathematica

Table[Mod[(2n)!!, (2n-1)!!], {n, 20}] (* Harvey P. Dale, Sep 23 2020 *)

Prog

(Python)
o=e=1
for n in range(1, 99, 2):
  o*=n
  e*=n+1
  print(str(e%o), end=', ')

Crossrefs

Cf. A006882, A122649, A129890, A232617.

Sequence in context: A184949 A132598 A257173 * A115892 A290329 A145531

Adjacent sequences: A232615 A232616 A232617 * A232619 A232620 A232621

Keyword

nonn

Author

Alex Ratushnyak, Nov 27 2013

Status

approved