It is 20.
-20 because -20 + 36 = 16
A single number cannot have a sum or a product - a sum or product is used to compare two or more numbers.
4 + 2*n â‰¥ 20
There aren't any numbers like that. You might be thinking of 28, which has a sum of all its factors equal to twice itself, making it a perfect number. Proper factors are a different set.
47 Impossible problem!