Definition of a perfect number

A perfect number, like 6 , is the sum of its proper divisors ( 6 = 3 r 2 r 1 = 3 + 6 + 1 )

The acient mathamaticians Nicomachus ( A.D. 60 - 120 ) knew of the first four:

6, 28, 496 and 8,128.

The next two are: 33,550,336 and 8,589,869,056.

All perfect numbers discovered thus far are even.