Find the missing number?

The missing number is 5.

The numbers in the sequence are all prime numbers, except for the missing number. The missing number must be a prime number that is not already in the sequence. The only prime number that fits this description is 5.

Here is a table of the prime numbers from 1 to 100:

1 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

As you can see, the only prime number that is not already in the sequence is 5. Therefore, the missing number is 5.