6! = 6*5*4*3*2*1 = 720
9999
100,000
512
12
24
There are 504 such numbers.
840
823543
There are 60480 numbers.
6
There are 5! = 120 such numbers.
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.