How it is calculated
Zero stays zero. For numbers divisible by 9, the digital root is 9, not 0.
For n > 0 the root = 1 + (n − 1) mod 9
Where the numbers come from
- Number
Example
3 + 8 = 11, then 1 + 1 = 2. The digital root of 38 is 2.
Questions
Is this the divisibility-by-9 check?
Yes. If the digital root is divisible by 9, so is the number. A root of 9 is exactly that case.
Negative numbers?
A nonnegative integer is used here.
Leading zeros?
The number is entered as a value, so leading zeros are not kept.