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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 8 18:37 EST 2019. Contains 329865 sequences. (Running on oeis4.)