

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
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OFFSET

1,2


COMMENTS

a(n) is divisible by A049606(n).  Robert Israel, Jan 28 2019


LINKS

Robert Israel, Table of n, a(n) for n = 1..403


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)+', ',


CROSSREFS

Cf. A006882, A049606, A122649, A129890, A232617, A232618, A306185.
Sequence in context: A152551 A012252 A262538 * A027723 A046265 A082705
Adjacent sequences: A306181 A306182 A306183 * A306185 A306186 A306187


KEYWORD

nonn


AUTHOR

Alex Ratushnyak, Jan 27 2019


STATUS

approved



