I'm reeeally liking this one! It's funny how, to save the world from the brink of destruction, you have to stop and play mathematical games with an AI.
My only gripe is that the factorial button is wrong? It seems to be taking the factorial of one number lower than it should; 7! should produce 5040, but it produces 720 instead, which is 6!. The same thing applies to 8!, too.
Besides that, this is a great one. We need more math games that really push people to think, and I'm a sucker for games that make me slow down to solve puzzles!