Common Divisibility Rules (1 through 12)
1: All whole numbers are divisible by 1.
2: The last digit is even (0, 2, 4, 6, or 8).
3: The sum of all the digits is divisible by 3.
4: The last two digits form a number divisible by 4.
5: The last digit is 0 or 5.
6: The number passes both the 2 rule and the 3 rule (it is even and its digit sum is divisible by 3).
7: Double the last digit and subtract it from the rest of the number; if the result is a multiple of 7 (or 0), the number is divisible by 7.
8: The last three digits form a number divisible by 8.
9: The sum of all the digits is divisible by 9.
10: The last digit is 0.
11: Subtract and add digits in alternating order from left to right (or find the difference between the sum of digits in odd places and even places); the result must be 0 or a multiple of 11.
12: The number passes both the 3 rule and the 4 rule. [1, 2, 3]