Reminds me of Bomberman for the original Nintendo Entertainment System. Maybe in the sequel, there will be codes to let you keep your powerups after dying.
Nice little game. A couple of suggestions:
Make the whole thing BIGGER.
Add a "pen vs pencil" for the numbers so we can make a spot unchangeable.
A way to "push" a cube up or down so we can see which square goes with which cube(s). (colorblind option?)