The Central American Olympiad is an annual competition. The ninth Olympiad is held in 2007. Find all the positive integers $n$ such that $n$ divides the number of the year in which the $n$-th Olympiad takes place.
1. We start by noting that the 9th Olympiad was held in 2007. This implies that the 1st Olympiad was held in \( 2007 - 8 = 1999 \).
2. Therefore, the \( n \)-th Olympiad is held in the year \( 1999 + (n-1) = 1998 + n \).
3. We need to find all positive integers \( n \) such that \( n \) divides the year in which the \( n \)-th Olympiad takes place, i.e., \( n \) divides \( 1998 + n \).
4. This condition can be written as:
   \[
   n \mid (1998 + n)
   \]
5. Since \( n \mid (1998 + n) \), it follows that \( n \mid 1998 \) (because \( n \mid n \) is always true).
6. Therefore, \( n \) must be a divisor of 1998. We now find all positive divisors of 1998.

To find the divisors of 1998, we first perform its prime factorization:
\[
1998 = 2 \times 3^3 \times 37
\]

7. The divisors of 1998 are all the products of the form \( 2^a \times 3^b \times 37^c \) where \( a \in \{0, 1\} \), \( b \in \{0, 1, 2, 3\} \), and \( c \in \{0, 1\} \).

8. Listing all combinations, we get the divisors:
\[
1, 2, 3, 6, 9, 18, 27, 54, 37, 74, 111, 222, 333, 666, 999, 1998
\]

Thus, the positive integers \( n \) such that \( n \) divides the number of the year in which the \( n \)-th Olympiad takes place are the divisors of 1998.

The final answer is \( \boxed{ \{1, 2, 3, 6, 9, 18, 27, 54, 37, 74, 111, 222, 333, 666, 999, 1998\} } \).