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

Author

Alex Ratushnyak, Nov 27 2013

Keywords

• nonn

Comments

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

Examples

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

Crossrefs

Cf. A006882, A122649, A129890, A232617.

Programs

Mathematica

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

Python

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

Formula

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