Byte Invaders

It's certainly educational (and without falling into the 'edutainment' trap of sandwiching the gameplay and educational content too)!

I wonder if there is a way to make it so that the player could shoot off bits (pun intended) of the enemy ship at a time rather than the whole ship, while maintaining the challenge.

Fun and challenging, but eventually I got bored in the wave-9 one and spammed random numbers :P But I had them 100% correct up to that point :D