Replace the question mark with the correct number.

2 + 2= 4
3 + 3= 18
4 + 4= ?

6 + 6= 180

48

2 + 2= 4 (2*2*1)
3 + 3= 18 (3*3*2)
4 + 4= 48 (4*4*3)
6 + 6= 180 (6*6*5)