digit sum

Noun

digit sum (plural digit sums)

1. The sum of all digits.
   • The digit sum of 517 is 5 + 1 + 7 = 13.
   • Given an integer X written in base 10 (as is usual), compute the sum of the digits of X: call the result the digit sum of X. If the digit sum is greater than 9, we form the digit sum again. Continue in this way to obtain the iterated digit sum which is at most 9.2004, J. F. Humphreys, M. Y. Prest, Numbers, Groups and Codes, Cambridge University Press, →ISBN, page 49
2. the number obtained when repeatedly applying above described operation until arriving at a single-digit number.
   • The digit sum of 517 is 4, since 5 + 1 + 7 = 13 and 1 + 3 = 4.
   • The definition is that to find the digit sum of any number, add all the digits in the number. If number is a one digit no. then stop else add all the digits in this new number. Continue this process till we get one digit number.2012, Kiran Parulekar, Amazing Properties of Squares & Their Calculations, Kiran Anil Parulekar, page 17