I enjoyed this. Overall it looks nice, simple design, executed well.
I would have preferred to enter the numbers at my own pace though... waiting a couple of seconds between number presses takes a little bit of the fun out of it I think. This way, you could measure speed as factor in overall score.
For example; Enter the correct number within 1 second for +10 points, with 2 seconds for +5 points, and later than that for +2 points...
Otherwise it's a great take on the theme :-)