I got it.
About thirty minutes of non-continuous free time and a half sheet of paper gave me this:
For any whole number "x":
1 digit: x
2 digits: (\left\lfloor\frac{x}{10}\right\rfloor) + (x -10(\left\lfloor\frac{x}{10}\right\rfloor))
...
After awhile, I realized I could combine like...