Help me find my game! Please!?

I'm trying to find a game that I played when I was younger. It's was a game that you would buy at the store and then download it on the computer. I think it was called Math Invaders. It was on a spaceship, and there were doors that would unlock, only if you got the math question correct. And to destroy the aliens you'd have to get a question correct. I loved this game. If you think you know what it is, could you please find a website that is selling it. Thanks!