Divisibility rule for 9

The sum of the digits is divisible by 9

e.g - Random number: 1897236. Then you have to add them all up - 1+8+9+7+2+3+6 =36... If you don't if 36 is divisible by 9, then add 3 and 6... 3+6=9. 9 is divisible by 9, so 1897236 is divisible by 9.

Random number: 37836547. 3+7+8+3+6+5+4+7= 43, 4+3= 7. 7 is not divisible by 9, so 37836547 is not divisible by 9.