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: 17, 51, and 153. Use division to check 7, 8, 11, and 13. Since $\displaystyle{153}\div{13}\usepackage{cmbright}\Huge\$ is less than 13, stop.