double

  • 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;

    }
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