A perfect number is a number that is equal to the sum of all its factors other than itself.
For example, the factors of 6 are 1 , 2 , 3 , and 6 . Since
1 + 2 + 3 = 6 ,
6 is a perfect number.
The next perfect number is 28 . The factors of 28 are 1 , 2 , 4 , 7 , 14 , and 28 , and
1 + 2 + 4 + 7 + 14 = 28 .
