Double factorial

The double factorial of a non-negative integer n, denoted by n!!, is defined as the product of all integers between 1 and nLaTeXn that have the same parity as nLaTeXn:

n!! ={leftn·(n-2)·(n-4)  4 · 2 if 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!!LaTeXn!!.

symbols.double_factorial.calc.png