There are 1 and itself in the divisor of any natural number, and we call the factor smaller than itself the true divisor of this natural number. For example, all true divisors of 6 are 1, 2 and 3, and 6 = 1+2+3. In this way, the sum of all true divisors of a number is exactly equal to this number, which is usually called a perfect number.

The ancient Greeks attached great importance to perfect numbers. After Pythagoras discovered it, people began to study the perfect number. Maybe there are too few perfect numbers. So far, mathematicians have found 29 perfect numbers, all of which are even numbers. The first five perfect numbers are: 6,28,496,8/kloc-0,28,33550336.

Perfect numbers have many interesting properties, such as the sum of continuous natural numbers:

6= 1+2+3

28= 1+2+3+4+5+6+7

8 128= 1+2+3+4……+ 127

===================================