Answer
$\{1,2,3,4,6,8,9,12,18,24,36,72\}$
Work Step by Step
To list the factors of a number, we list all of the whole numbers that we can multiply to get the number. In the case of the number $72$, the factors are $\{1,2,3,4,6,8,9,12,18,24,36,72\}$.