Find the missing number?

The missing number is $\boxed{11}$.

The numbers in the sequence are all prime numbers, except for the missing number. The missing number must be a prime number that is less than 17, since the numbers in the sequence are all less than 17. The only prime number that is less than 17 and is not in the sequence is 11. Therefore, the missing number is 11.

Here is a list of all the prime numbers less than 17:

• 2
• 3
• 5
• 7
• 11
• 13
• 17

As you can see, 11 is the only prime number that is not in the sequence. Therefore, the missing number is 11.