For example, the number 6 has proper divisors 1, 2, and 3. The sum of these proper divisors is 6, and so 6 is a perfect number.
The first three perfect numbers are 6 = 1 + 2 + 3,
28 = 1 + 2 + 4 + 7 + 14, and
496 = 1 + 2 + 4 + 8 + 16 + 31 + 62 + 124 + 248.
