Correct Answer: 15

Solution : Let's check the options –
First option: 15→The factors of 15 are 1, 3, 5, 15. This means that 15 is a composite number as it has more than 2 factors.
Second option: 17→The factors of 17 are 1, 17; 17 is a prime number.
Third option: 19 → The factors of 19 are 1, 19; 19 is a prime number.
Fourth option: 13→The factors of 13 are 1, 13; 13 is a prime number.

So, the first option does not follow a similar pattern as the other three options. Hence, the first option is correct.