9
1
7
13
Answer is Wrong!
Answer is Right!
The missing number is 1.
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 in the sequence. The only prime number that is not in the sequence is 1.
The sequence is also increasing by 2 each time. The missing number must be a prime number that is 2 more than the previous number in the sequence. The only prime number that is 2 more than the previous number in the sequence is 1.
Therefore, the missing number is 1.