This can be done with simple concept of PERMUTATIONS AND COMBINATIONS.
The number can arrange themselves repeatedly to form different numbers. The possible number of ways they can do so is 3×2×1=6
3
×
2
×
1
=
6
ways.
ALTER,
You can arrange these number in 3!
3
!
ways, which finally produces the same result i.e 3!=3×2×1=6
3
!
=
3
×
2
×
1
=
6
ways.