What numbers are perfect numbers

A perfect number is a number where the sum of its divisors is equal to the number.

For example 6: 1 + 2 + 3 = 6

Another example is 28: 1 + 2 + 4 + 7 + 14 = 28

Here is a short list of perfect numbers: 6, 28, 496, 8128, 33550336, and the numbers get way bigger as we go on.