Question

A perfect number is:

• A. a number whose sum of its digits is equal to the product of its digits.
• B. a number whose sum of factors is equal to twice the number.
• C. a number whose sum of factors is equal to thrice the number.
• D. a number which is co-prime to every other number.

Answer 1

The correct option is B

a number whose sum of factors is equal to twice the number.

A perfect number is a number for which the sum of all its factors is equal to twice the number.

For example, 6 is a perfect number since the sum of its factors 1, 2, 3 and 6 is 12 i.e. twice of 6.

Perfect numbers are also defined as those numbers that equal the sum of all their factors including 1 but excluding the number itself.

Taking the same example of 6: sum of its factors excluding the number itself i.e 6 = 1+2+3 = 6.