Divisibility rules to take the pain out of dividing big numbers
On computers, they come in handy when you have to handle numbers bigger than int or long as strings.
1: skip
2: the ones digit is a multiple of 2
3: the sum of all digits is a multiple of 3
4: the last two digits are 00 or a multiple of 4
5: the ones digit is 0 or 5
6: divisible by 2 && divisible by 3
7:
8: the last digits are 000 or a multiple of 8
9: the sum of all digits is a multiple of 9
10: the ones digit is 0
11: (sum of odd-position digits - sum of even-position digits) is a multiple of 11