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A175430 a(n) = (n-1)! * (n+1)!. 2

%I

%S 2,6,48,720,17280,604800,29030400,1828915200,146313216000,

%T 14485008384000,1738201006080000,248562743869440000,

%U 41758540970065920000,8142915489162854400000,1824013069572479385600000

%N a(n) = (n-1)! * (n+1)!.

%F a(n) = (Product_{k=1..n} k*A020725(k)) / n;

%F a(n) = (Product_{k=1..n} k*(k+1)) / n.

%F a(n) = (-1) * A129464(n) = A179442(n) * n. [_Jaroslav Krizek_, Jul 22 2010]

%F a(n) = 2*A010791(n-1). - _Michel Marcus_, Feb 03 2016

%e a(5) = (5-1)! * (5+1)! = 4! * 6! = 24 * 720 = 17280.

%e a(5) = ((1*2) * (2*3) * (3*4) * (4*5) * (5*6)) / 5 = 17280.

%t #[[1]]*#[[3]]&/@Partition[Range[0,20]!,3,1] (* _Harvey P. Dale_, Jun 20 2017 *)

%o (PARI) a(n) = (n-1)! * (n+1)!; \\ _Michel Marcus_, Feb 03 2016

%K nonn

%O 1,1

%A _Jaroslav Krizek_, May 10 2010

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Last modified October 20 05:42 EDT 2017. Contains 293601 sequences.