Take a number.
Square it.
Now take the number that is one less than the first ORIGINAL number.
Square it.
Subtract them.

Then add the bases you just used.
Weird!!
I just wanna say I thought of this during my math exam a couple of days ago, and I'm very, very proud of my nerd skills.

EXAMPLE OF MY THEORY:
2-squared - 1-squared
= 4 - 1
= 3

2 + 1 = 3

And it works with everything!!

5-squared - 4-squared
= 25 - 16
= 9

5 + 4 = 9

...etc., etc., etc.

You gotta love it.