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a(n) = (2n)!! mod (2n-1)!! where k!! = A006882(k).
4

%I #15 May 03 2021 15:36:51

%S 0,2,3,69,60,4500,104580,186795,13497435,442245825,13003053525,

%T 64585694250,3576632909850,147580842959550,5708173568847750,

%U 27904470362393625,2292043480058957625,126842184377462428875,6371504674680470700375,312265748715684068930625

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

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

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

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

%t Table[Mod[(2n)!!,(2n-1)!!],{n,20}] (* _Harvey P. Dale_, Sep 23 2020 *)

%o (Python)

%o o=e=1

%o for n in range(1,99,2):

%o o*=n

%o e*=n+1

%o print(str(e%o), end=',')

%Y Cf. A006882, A122649, A129890, A232617.

%K nonn

%O 1,2

%A _Alex Ratushnyak_, Nov 27 2013