28 = 2 x 2 x 7
2 + 2 + 7 = 11
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4 and 2 are factors of -28.
The sum of all the positive factors of 12 is 28.
28
A perfect number is a number that is the sum of all its proper factors (that is all its factors excluding itself). The next perfect number after 28 is 496
The second perfect number after 6 is 28. The sum of the factors of 28, excluding itself, is 1 + 2 + 4 + 7 + 14 = 28.