Jaison N. answered 09/07/12
A PhD to Teach You Math
Factoring integers is like trying to break down an integer into its different building blocks. And there are a number of little rules that you can memorize that can help you with finding factors other than 1 and the number you want to factor.
For example, if a number is even, then 2 is a factor. So 28 = 14 x 2. But wait! 14 is also even so repeat the rule. 14 = 2 x 7. And we know that we can't break down 2 or 7.
Now, write out what you have: 28 = 2 x 7 x 2. Ahh, we see that our factorization has 2 x 2 = 4, so 4 is also a factor.
Another rule: Lets say you have 3,457,000. Count the number of zeroes, pull them out and throw in a 1:
3,457,000=3457 x 1000. Oh wait, use the first rule again: 1000 = 2 x 500. Oh wait 500 is even, use it again: 500 = 2 x 250. I'm not doing anything exceptionally difficult here except for the simplest thing possible. And I'm repeating it over and over again.
There are other rules that you can memorize that will HELP you do these problems. You still need to do some work when you are learning how to do this stuff.