Find the missing number?

7
17
5
11

The answer is 11.

The numbers in the sequence are all prime numbers, except for 10, which is a composite number. The missing number must be a prime number that is greater than 10 and less than 17. The only prime number that meets these criteria is 11.

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A composite number is a natural number greater than 1 that is not prime.