Question

In the answer of Question Number 139 it is written -

By definition, a number, for which the sum of all its factors excluding the number itself is equal to twice the number, is called perfect number.

Should it be as below -

a number, for which the sum of all its factors excluding the number itself is equal to the number, is called perfect number.

Answer 1

Yes. You are correct it should be as given by you. A perfect number is a number for which the sum of all its factor excluding the number itself is equal to the number.
6 is a perfect number. The factors of 6 are 1,2,3 & 6.

1+2+3 = 6

Similarly for 28 its factors are 1, 2, 4, 7 and 14

1 + 2 + 4 + 7 + 14 =28
28 is a perfect number.