The missing number is 19.
The numbers in the sequence are all prime numbers, except for 12, which is a composite number. 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.
The sequence starts with 2, which is the first prime number. The next number in the sequence is 3, which is the second prime number. The third number in the sequence is 5, which is the third prime number. The fourth number in the sequence is 7, which is the fourth prime number. The fifth number in the sequence is 11, which is the fifth prime number. The sixth number in the sequence is 13, which is the sixth prime number. The seventh number in the sequence is 17, which is the seventh prime number. The eighth number in the sequence is 19, which is the eighth prime number.
The sequence continues in this way, with each number being the next prime number after the previous number. The missing number in the sequence is 19, which is the eighth prime number.