A perfect number is one whose factors add up to the number.

These are quire rare. The first one is 6:

6 = 1 + 2 + 3

There are only two more less than a thosand, and not many more known at all (even with extensive computer searches). But the second perfect number is less than 32. See if you can find it.

You should note that (I think) all perfect numbers are even.