# What is a perfect number?

A perfect number is a whole number, an integer greater than zero; and when you add up all of the factors less than that number, you get that number.

**Examples:**

The factors of 6 are 1, 2, 3 and 6.

1 + 2 + 3 = 6

The factors of 28 are 1, 2, 4, 7, 14 and 28.

1 + 2 + 4 + 7 + 14 = 28

The factors of 496 are 1, 2, 4, 8, 16, 31, 62, 124, 248 and 496.

1 + 2 + 4 + 8 + 16 + 31 + 62 + 124 + 248 = 496

The factors of 8128 are 1, 2, 4, 8, 16, 32, 64, 127, 254, 508, 1016, 2032, 4064 and 8128.

I’ll let you add them up.

According to The Merriam-Webster Dictionary, the term was first used in the fourteenth century. The Grolier Multimedia Encyclopedia says that perfect numbers are “another example of Greek progress in number theory,” and credits the Pythagoreans for coining the term “perfect.” If you are interested in learning more about “perfect” numbers, you should also read up about “Mersenne” prime numbers because they are closely related.

The first four perfect numbers were known over 2,000 years ago. Some ancient cultures gave mystic interpretations to numbers that they thought were magic.