What is divisibility rule of 13?

Answer 1

Add four times the last digit to the remaining leading truncated number. If the result is divisible by 13, then so was the first number. Apply this rule repeatedly as necessary.

Here is an example.

You want to know if 50661 is divisible by 13. Add 4 times the last digit to the remaining numbers you have after removing the last digit. So we add 1x4=4 to the number we have after taking the 1 after 50661. This is 5066+4=5070. Now do this again. 4x0 is 0 and add this to the number you get by taking 5070 and truncating the number.. ie drop the last 0.

So we have 507+0=507.

Now add 7x4=28 so 50. Of course 50 comes from 507 after dropping the 7.

You have 78. Now since 78 is 6x13, the original number must have been divisible by 13 too.

This is one of the more complicated divisibility rules.