login
A227415
a(n) = (n+1)!! mod n!!.
1
0, 0, 1, 2, 7, 3, 9, 69, 177, 60, 2715, 4500, 42975, 104580, 91665, 186795, 3493665, 13497435, 97345395, 442245825, 2601636975, 13003053525, 70985324025, 64585694250, 57891366225, 3576632909850, 9411029102475, 147580842959550, 476966861546175, 5708173568847750
OFFSET
0,4
COMMENTS
a(n) is divisible by A095987(n+1), and is nonzero for n > 1. - Robert Israel, Mar 10 2016
LINKS
FORMULA
a(n) = A006882(n+1) mod A006882(n).
EXAMPLE
a(4) = 5*3 mod 4*2 = 15 mod 8 = 7.
MAPLE
seq(doublefactorial(n+1) mod doublefactorial(n), n=0..100); # Robert Israel, Mar 10 2016
PROG
(Python)
for n in range(2, 77):
prOdd = prEven = 1
for i in range(1, n, 2): prOdd *= i
for i in range(2, n, 2): prEven *= i
if n&1: print str(prEven % prOdd)+', ',
else: print str(prOdd % prEven)+', ',
CROSSREFS
Cf. A007911: (n-1)!! - (n-2)!!
Cf. A007912: (n-1)!! - (n-2)!! (mod n).
Cf. A060696: (n-1)!! + (n-2)!! except first two terms.
Sequence in context: A021369 A340711 A242304 * A361207 A309156 A298042
KEYWORD
nonn,easy
AUTHOR
Alex Ratushnyak, Jul 10 2013
STATUS
approved