先分解素因数,84=2*2*3*7,所以经过排列组合相乘,因数有1,2,3,7,4,6,14,21,12,28,42,84 .同理,120=2*2*2*3*5,因数有1,2,3,5,2,6,15,8,12,20,30,24,40,60,120 .200=2*2*2*5*5,因数有1,2,5,4,10,8,20,50,40,100,200 ....