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A232618
a(n) = (2n)!! mod (2n-1)!! where k!! = A006882(k).
4
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.
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
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Nov 27 2013
STATUS
approved