Input (grade 8): Since six equals the sum of these proper divisors, six is the smallest perfect number, Granville number, and - perfect number. As a perfect number, 6 is related to the Mersenne prime 3, since 21 (22 - 1) = 6.
Output (grade 9): Six is also the first perfect number which means that the sum of its factors (1, 2 and 3) are equal to the number itself (6).