The divisibility rules can be used to show that 1, 3 and 9 are factors (and that 2, 4, 5, 6, 10 and 12 are not). Use factor pairs to find the rest of the factors: 13, 39, and 117. Use division to check 7 and 8. Since $\displaystyle{117}\div{12}\usepackage{cmbright}\Huge\$ is less than 12, stop.