Definition of perfect numbers in math. A perfect number is any number that... A perfect number: a number is perfect when the sum of its divisors (except the number itself) equals the given number. 6 : The divisors of 6 are 1,2,3 & 6. To show that this is a perfect number we could all the divisors except the number itself 1+2+3 = 6. 28 1 + 2 + 4 + 7 + 14 =28. 496 and 8128 are also perfect number.