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A227415
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a(n) = (n+1)!! mod n!!.
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1
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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
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OFFSET
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0,4
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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a(4) = 5*3 mod 4*2 = 15 mod 8 = 7.
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MAPLE
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seq(doublefactorial(n+1) mod doublefactorial(n), n=0..100); # Robert Israel, Mar 10 2016
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PROG
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(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)+', ',
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CROSSREFS
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Cf. A007912: (n-1)!! - (n-2)!! (mod n).
Cf. A060696: (n-1)!! + (n-2)!! except first two terms.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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