Which of the following numbers are prime numbers?  $137$~ ~ ~ ~ ~ ~ ~ ~ ~$151$~ ~ ~ ~ ~ ~ ~ ~ ~$237$~ ~ ~ ~ ~ ~ ~ ~ ~$301$ 
Overseas Competition->Knowledge Point->Number Theory Modules->Prime and Composite Numbers
$3$ is the factor of $237$ because $3 \times79 = 237$; $7$ is the factor of $301$ because $7 \times 43 = 301$. 