I know: * 2 - if it ends in 0,2,4,6,8, it's divisible by 2 * 3 - if the sum of the digits is divisible by 3, so is the number * 4 - Ignore everything but the

I know: * 2 - if it ends in 0,2,4,6,8, it's divisible by 2 * 3 - if the sum of the digits is divisible by 3, so is the number * 4 - Ignore everything but the last 2 digits. If the last 2 digits make a number that's divisible by 4, the whole number is (eg. anything ending in 52 is divisible by 4 because 52 is divisible by 4) * 5 - If it ends in 0 or 5, it's divisible by 5. * 6 - do an and of the 2 and 3 tests. * 8 - Same as the 4 test, only last 3 digits. * 9 - same as 3, only the digit sum needs to be divisible by 9 instead of 3 * 10 - If it ends in 0, it's divisible by 10. So I guess the only one I don't know is 11.