cross sum (crossfoot) of 21730 twentyonethousandsevenhundredthirty
The cross sum of 21730 is:
13
What is the cross sum / crossfoot of a number
The cross sum of a number is the sum of all digits of a natural number. In this case, all the digits of a number are added.
The sum of the digits is used, for example, in the check digit of the ISBN. However, there are many other mathematical functions and calculation methodologies that are based on the sum of the digits of a number.