Among the numbers provided, the only prime number is 29.
To determine if a number is prime, we need to check if it is divisible by any number other than 1 and itself. Let's analyze each number:
1. 18: This number is not prime because it is divisible by 2, 3, 6, and 9, in addition to 1 and 18.
2. 29: This number is prime because it is only divisible by 1 and 29. There are no other numbers that evenly divide it.
3. 40: This number is not prime because it is divisible by 2, 4, 5, 8, 10, 20, and 40, in addition to 1.
4. 27: This number is not prime because it is divisible by 3, 9, and 27, in addition to 1.
Therefore, the only prime number among the given options is 29.