Arithmetic & Basics
Basic

Divisibility by 9

A number is divisible by 9 if its digit sum is.

Formula

digit sum divisible by 9\text{digit sum divisible by 9}

Variables

digitsNumber digits

Example

729: 7+2+9=18 ✓

Did You Know?

The digits of any multiple of 9 always sum to a multiple of 9, the basis of the old "casting out nines" error check.

divisibility