What is the sum of the factors of 21?

To answer this question, we first need to work out the factors of 21. These are the whole numbers which multiply to make 21. 

We know that 1 multiplies with 21 to make 21, so they are both factors. 

2 is not a factor of 21, because we cannot multiply it with another whole number to make 21.

3 is a factor of 21, because it multiplies with 7 to make 21. 

Therefore the factors of 21 are 1, 3, 7 and 21. 

All that is left to do is to work out the sum of these numbers, that is to add them all up. 

21+1 + 3 +7 = 32

Therefore, the sum of the factors of 21 is 32. 

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