## factorial

• ### Double Factorial

The double factorial is a mathematical operation defined recursively as:
$n!!=\left\{\begin{matrix}1\ if\ n\leq 0\\n(n-2)!!\ otherwise \end{matrix} \right.$
eg.
$\textit{8!!=8*6*4*2*1= 384 }$
An algorithm can be implemented very simply in a recursive way, where the method calls itself many times. That is an implementation:

public static long doubleFact(long n){
if(n>=52)return 0;
if(n<=0)
return 1;
else
return doubleFact(n-2)*n;

}