4
3
7
1
Answer is Wrong!
Answer is Right!
The missing number is 7.
The numbers in the sequence are all prime numbers, except for 1. 1 is not a prime number because it is divisible by itself and by 1. The other numbers in the sequence are all divisible only by themselves and by 1.
Therefore, the missing number must be a prime number that is not already in the sequence. The only prime number that meets this criteria is 7.