# Perfect number

A perfect number is a number for which the sum of its proper factors is equal to the number itself.

### proper factor

The proper factors of a number are all its factors except the number itself.

Example

6 is a perfect number because the sum of its proper factors (1, 2, and 3) is equal to 6.

### Did you know?

Perfect numbers have been studied since ancient times. The early Egyptians are believed to have studied perfect numbers. Pythagoras, a famous Greek mathematician and philosopher, studied them, perhaps from a metaphysical (nonphysical) as well as a mathematical perspective. There is still much to learn about perfect numbers, and mathematicians still study them today.