Find the missing number?

3
4
7
2

The missing number is 7.

The numbers in the sequence are all prime numbers, except for 2, which is a composite number. The sequence starts with 2, and each subsequent number is 2 more than the previous number. Therefore, the missing number is 2 + 6 = 7.

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.