Digital root is the recursive sum of all the digits in a number. Given n, take the sum of the digits of n. If that value has more than one digit, continue reducing in this way until a single-digit number is produced. The input will be a non-negative integer. Examples 16 --> 1 + 6 = 7 942 --> 9 + 4 + 2 = 15 --> 1 + 5 = 6 132189 --> 1 + 3 + 2 + 1 + 8 + 9 = 24 --> 2 + 4 = 6 493193 --> 4 + 9 + 3 + 1..
