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Factorial2
n!! gives the double factorial of n.
Mathematical function (see Section A.3.10). . is a product of even numbers for even, and odd numbers for odd. See Section 3.2.5. See also: Gamma. New in Version 1.
Further Examples
n!! gives the double factorial of n. Mathematical function (see Section A.3.10). 
. 
is a product of even numbers for 
even, and odd numbers for 
odd. See Section 3.2.5. See also: Gamma. New in Version 1.
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