Working out all possible combinations

I worked out the rule of working out the possible combinations like this:

All combinations of 1 number = 6

All possible combinations of 2 numbers = 6*5 = 30

All possible combinations of 3 numbers = 30*4 = 120

All possible combinations of 4 numbers = 120*3 = 360

All possible combinations of 5 numbers = 360*2 = 720

All possible combinations of 6 numbers = ?

If I carry on the rule I end up with 720 * 1, which surely isn't right. Can anyone tell me how to work out the next number?

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