How many different four-digit numbers can be made using the digits 1, 2, 3, 4, 5, 6 if no digit can be used more than once?

In the first digit, there are 6 possibilities. In the second, there are 5, because you can't use the digit you used before. In the third, there are 4, and in the fourth, there are 3. So, 

6*5*4*3=360

There are 360 different possible four-digit numbers

What's the denominator

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