How many unordered pairs of prime numbers have a sum of 40?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
How many unordered pairs of prime numbers have a sum of 40?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
3
How many unordered pairs of prime numbers have a sum of 40?
train