2. In a candy store, candies are sold in three types of packages: small packs contain 6 candies, medium packs contain 9 candies, and large packs contain 20 candies. If you can only buy whole packs of candies, what is the maximum number of candies you cannot purchase?
2. Write non-negative integers in the following six-row number table:
\begin{tabular}{ccccccccc}
$\mathbf{0}$ & 6 & 12 & 18 & 24 & 30 & 36 & 42 & 48 \\
1 & 7 & 13 & 19 & 25 & 31 & 37 & 43 & 49 \\
2 & 8 & 14 & 20 & 26 & 32 & 38 & 44 & 50 \\
3 & 9 & 15 & 21 & 27 & 33 & 39 & 45 & 51 \\
4 & 10 & 16 & 22 & 28 & 34 & 40 & 46 & 52 \\
5 & 11 & 17 & 23 & 29 & 35 & 41 & 47 & 53
\end{tabular}

Each row of numbers increases by 6 from left to right.
If a number in a row can be obtained (i.e., you can buy this number of candies), then all the numbers in this row that come after it can also be obtained. Therefore, it is only necessary to find the first number in each row that can be obtained (which can be expressed in the form $9k + 20l$ where $k, l \in \mathbf{N}$), which are marked in bold in the table.
Clearly, the largest of these six numbers is 49.
Thus, the number 43, which is in the same row and immediately before it, is the largest number that cannot be obtained.