What's the problem? Suppose you've got a 144, a 72, a 36 and an 18 - that's already 4 spaces occupied and the remaining 5 numbers may not have a combination that adds up to 1.
There are 25 undos, but to get more you have to watch horrible ads or pay $.99.
I want to like this game, but cannot.
The best 9-themed point scoring puzzle app: NineOut, which I reviewed about 3 years ago. That's one of my favorite point scoring puzzle apps.