Correct Answer: 87

Solution : Let's check the options –
First option: 13→The factors of 13 are 1 and 13. So, 13 is a prime number.
Second option: 17→The factors of 17 are 1 and 17. So, 17 is a prime number.
Third option: 29→The factors of 29 are 1 and 29. So, 29 is a prime number.
Fourth option: 87→The factors of 87 are 1, 3, 29 and 87. So, 87 is not a prime number.

Hence, the fourth option is correct.