9x9x8x7x6x5x4x3
=1632960
763920
757
24
500
There are 5*4*3 = 60 such numbers.
With repeated digits, 43 = 64 Without repeated digits, 4*3*2 = 24
1 set
The answer will depend on how many digits you have at your disposal. Working with the 10 digits, and barring leading zeros, there are 8,877,690 numbers.
162
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
1
36