Context may be all you need

Project Euler meets Powershell - factorial...

function factorial {

[cmdletbinding()]
param([int64] $x)
	if ($x -lt 1) {
		return "Has to be on a positive integer"
	}
	if ($x -eq 1) {
		[int64] $x
	} else {
		[int64] $x * (factorial ($x-1))
	}
}