Factorial and Double Factorial

Let $n$ be a non-negative integer number, this application calculates the factorial of $n$ \[n!=n(n-1)(n-2)\cdots 2\cdot 1\] and double factorial \[ n!! = \left\{ \begin{array}{ll} \displaystyle \prod_{k=1}^{\frac{n}{2}}(2k)=n(n-2)(n-4)\cdots 4\cdot 2 & \text{for even } n \\ \displaystyle \prod_{k=1}^{\frac{n+1}{2}}(2k-1)=n(n-2)(n-4)\cdots 3\cdot 1 & \text{for odd } n \end{array} \right. \] Note that $n!!$ is not the same as $(n!)!$, for example, $4!!=4\cdot 2=8 $ but $(4!)!=24!=620448401733239439360000$

Factorial and Double Factorial Calculator