And this thing right over here is exactly what we wrote over here. This is equal to, this is equal to n factorial. But if we directly applied this formula, if we applied this formula, this would need to be n factorial over n minus n factorial. And then you might see why this is interesting because this is going to be n factorial over zero factorial. So in order for this formula to apply for even in the case where k is equal to n, even in the case where k is equal to n, which is this one right over here, and for that to be consistent with just plain old logic, zero factorial needs to be equal to one. And so the mathematics community has decided, hey, this thing we've constructed called factorial, you know, we've said, hey, you put an exclamation mark behind something. In all of our heads, we say you kind of count down that number all the way to one and you keep multiplying them.