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.