FactorialL function
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Namespace: Microsoft.Quantum.Math
Package: Microsoft.Quantum.Standard
Returns the factorial of a given integer.
function FactorialL (n : Int) : BigInt
Input
n : Int
The number to take the factorial of.
Output : BigInt
The factorial of the provided input.
Remarks
This function returns exact factorials for arbitrary-size integers, using a recursive decomposition into double-factorials ($n!!$). In particular, if $n = 2k + 1$ for $k \in \mathbb{N}$, then: $$ n! = n!! \times k! \times 2^k, $$ where $k!$ can be computed recursively. If $n$ is even, then we can begin the recursion by computing $n! = n \times (n - 1)!$.
See Also
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