Divisibility Rules
Some handy rules for division. Handy when trying doing factorization!
From Dr. Math:
2 If the last digit is even, the number is divisible by 2.
3 If the sum of the digits is divisible by 3, the number
is also.
4 If the last two digits form a number divisible by 4,
the number is also.
5 If the last digit is a 5 or a 0, the number is divisible
by 5.
6 If the number is divisible by both 3 and 2, it is also
divisible by 6.
7 Take the last digit, double it, and subtract it from the
rest of the number; if the answer is divisible by 7
(including 0), then the number is also.
8 If the last three digits form a number divisible by 8,
then the whole number is also divisible by 8.
9 If the sum of the digits is divisible by 9, the number
is also.
10 If the number ends in 0, it is divisible by 10.