2002 Gauss 7 Problem 18

A perfect number is an integer that is equal to the sum of all of its positive divisors, except itself. For example, 28 is a perfect number because 28 = 1+2+4+7+14. Which of the following is a perfect number?

\textbf{(A)}\ 10\quad \textbf{(B)}\ 13\quad \textbf{(C)}\ 6\quad \textbf{(D)}\ 8\quad \textbf{(E)}\ 9

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Gauss contests here.