Very Good
It makes extremely good fun out of a simple concept, and that's what I like in a flash game. However, it got just a slight bit repetitive. Also, the huger numbers like 110 and 155 are almost impossible to destroy if there's also tons of other numbers coming at you. Maybe make it so pressing 4 take off 10? Something like that. Also, it would be cool if there were 'division enemies' that divided themselves into 2 regulars with half the value (rounded up for odds) if hit with a with a 3, split 3-way, again, either rounded up or down. I have virtually no experience with flash of actionscript, but that would be extremely cool if it's possible.
Still, excellent work (much better than I could do)