Factorial with PowerShell

Get-Factorial.ps1

function Factorial ([bigint]$x)
{
    if ($x -ge 1)
    {
        return $x * (Factorial ($x = $x - 1))
    }
    elseif ($x -eq 0)
    { 
        return 1 
    }
     else
    {
        throw "NaN"
    } 
}

Thanks for posting