9.2. Find the maximum odd natural number that cannot be represented as the sum of three distinct composite numbers.
Answer: 17.

Solution: An odd number gives a remainder of 1 or 3 when divided by 4. In the first case, the desired representation has the form \( n = 4k + 1 = 4(k-4) + 8 + 9, k \geq 5, n \geq 21 \), in the second case - \( n = 4k + 3 = 4(k-3) + 6 + 9, k \geq 4, n \geq 19 \). On the other hand, the three smallest composite numbers are 4, 6, 8, the sum of which is 18, so the number 17 cannot be represented in the required form. It is the answer to the problem.

Grading: Simply providing the answer with verification: 0 points. Failure to justify the non-representability of 17 in the desired form - minus 2 points.