[how to draw random circles f.e. backgrounds]

Hello,

i want to draw random circles for a backgroundimage. I know the power duplicate tool - so i can quickly draw a lot of circles in row and colums. But i also want that the circles have a litte random size. Can i do this also with the "power duplicate"? I think, i onec saw a tutorial, where you can type something in the transform panel to achieve random sizes during the power duplicate.

Would be glad if someone can help me out, thankx