Nine different two-digit numbers can be formed with the digits 1, 3 and 7. How many of these numbers are prime?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Nine different two-digit numbers can be formed with the digits 1, 3 and 7. How many of these numbers are prime?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
7
Nine different two-digit numbers can be formed with the digits 1, 3 and 7. How many of these numbers are prime?
train