Thursday, February 16, 2006
Here's another mathematical shortcut. If you didn't already know it, I hope it saves you some time!
1. add the digits together.
2. if there is more than one digit in the sum and you are not sure if the sum is divisible by 3, just add the digits together again. This converges quickly to a number that is obviously divisible or not divisible by 3.
3. If the resultant sum is divisible by 3, the original integer is divisible by 3. If it isn't, neither is the original.
So there you have it.