If you make a sequel one element you should use is if a number goes past 10 you could make it so the excess is trimmed off.
Lets say we had a 4 a 7 and a 9, we could add the 4 to the 7 for 11 and trim off the 1 to add to the 9 or 4+9=13=10+3+7=10 the other way around.