7. (10 points) On the blackboard, there are 2013 numbers from 1 to 2013. Each time, you can erase two of these numbers and write down the digital sum of their sum. Continue this process until there are four numbers left on the blackboard, and their product is 27. What is the sum of these four numbers? $\qquad$ .
【Solution】Solution: According to the analysis, the remainder of a number divided by 9 is equal to the remainder of the sum of its digits divided by 9. Each operation changes the sum of the number to the sum of its digits, without changing the remainder when divided by 9. $1+2+3+\cdots+2013=2014 \times 2013 \div 2$ $=1007 \times 2013$,

Thus, the sum of the remaining four numbers, when divided by 9, also leaves a remainder of 3. Decomposing 27 into the product of four numbers, $27=3 \times 3 \times 3 \times 1=3 \times 9$ $\times 1 \times 1=27 \times 1 \times 1 \times 1$,

The sums are $10, 14, 30$, respectively. Only 30 leaves a remainder of 3 when divided by 9, so the sum of these numbers is 30. Therefore, the answer is: 30.