The sum of digits of n (also known as the digit sum of n) is, well, the sum of the digits of n. For example, the sum of digits of the number 123 is 1 + 2 + 3 = 6.
def digit_sum(n):
total = 0
while n > 0:
//Note that you can replace 10 with any base you want.
total += n % 10 //n % 10 gives you the last (least significant) digit.
n = n / 10 //Dividing by ten chops that last digit off.
return total