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A306184
a(n) = (2n+1)!! mod (2n)!! where k!! = A006882(k).
2
1, 7, 9, 177, 2715, 42975, 91665, 3493665, 97345395, 2601636975, 70985324025, 57891366225, 9411029102475, 476966861546175, 20499289200014625, 847876038362978625, 35160445175104123875, 1487419121780448231375, 945654757149212735625, 357657177058846280240625
OFFSET
1,2
COMMENTS
a(n) is divisible by A049606(n). - Robert Israel, Jan 28 2019
LINKS
FORMULA
a(n) = A006882(2*n+1) mod A006882(2*n).
EXAMPLE
a(3) = A006882(7) mod A006882(6) = (7*5*3) mod (6*4*2) = 105 mod 48 = 9.
MAPLE
f:= n -> doublefactorial(2*n+1) mod doublefactorial(2*n):
map(f, [$1..40]); # Robert Israel, Jan 28 2019
PROG
(Python)
o=e=1
for n in range(2, 99, 2):
o*=n+1
e*=n
print str(o%e)+', ',
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Jan 27 2019
STATUS
approved