SOLUTION: How many number sequences can you get using only the numbers from 1 through 9 and that is only 6 digits long?

Choose the 1st digit any of the 9 ways.
For each of those ways, we can choose the 2nd digit any of the 8 remaining ways.
For each of those ways, we can choose the 3rd digit any of the 7 remaining ways.
For each of those ways, we can choose the 4th digit any of the 6 remaining ways.
For each of those ways, we can choose the 5th digit any of the 5 remaining ways.
For each of those ways, we can choose the 6th digit any of the 4 remaining ways.

Answer 9×8×7×6×5×4 ( to 6 factors) = 9P6 =  =  = 9*8*7*6*5*4 = 60480

Easiest formula is start with 9 and multiply by 1 less, then 1 less than that,
and so on till you have 6 factors.

Edwin