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Double factorial
Reading time: 1minThe double factorial of a non-negative integer n, denoted by n!!, is defined as the product of all integers between 1 and n that have the same parity as n:
n!!=n·(n-2)·(n-4)⋯4·2if n is even
n·(n-2)·(n-4)⋯3·1if n is odd
0!!=1 by convention.
Syntax
Integer!!
Description
Given an integer between 1 and 65535, returns n!!.
