Double factorial
= Double factorial
{wiki=Double_factorial}
The double factorial, denoted by \\( n!! \\), is a mathematical operation that is defined for non-negative integers. It is the product of all the integers from \\( n \\) down to 1 that have the same parity (odd or even) as \\( n \\). Specifically, it is defined as follows: 1. For an even integer \\( n = 2k \\): \\\[ n!! = 2k!!