Answer:

A whole number is a perfect number when it is equal to the sum of all its factors (not including itself). The two smallest perfect numbers are 6 and 28.

6 = 1 + 2 + 3 and 28 = 1 + 2 + 4 + 7 + 14
Very few perfect numbers are known. The next three are 496, 8128 and 33 550 336

Here shows few examples of perfect numbers:
6 = 2¹ (2² - 1) = 1 + 2 + 3,
28 = 2² (2³ - 1) = 1 + 2 + 3 + 4 + 5 + 6 + 7 = 1³ + 3³,
496 = 2⁴ (2⁵ - 1) = 1 + 2 + 3 + ... + 29 + 30 + 31 = 1³ + 3³ + 5³ + 7³