Is there a classification system where the sum of the digits are a factor?

Question

This may be confusing. An example:

12

1+2=3

3 is a factor of 12.

135

1+3+5=9

9 is a factor of 135.

555

5+5+5=15

15 is a factor of 555.

What is the name of this classification system or did I create a new one?

Answer 1

These are called Harshad Numbers (or Niven numbers).

In mathematics, a harshad number (or Niven number) in a given number base is an integer that is divisible by the sum of its digits when written in that base.