3. Replacing the larger number of two different natural numbers with the difference between these two numbers is called one operation. For example, for 18 and 42, such operations can be performed continuously. Thus, we have: $18,42 \rightarrow 18,24 \rightarrow 18,6 \rightarrow 12$, $6 \rightarrow 6,6$, until the two numbers are the same. Try to give the two smallest five-digit numbers, such that, following the above operation, the final identical number is 15. These two five-digit numbers are $\qquad$ and $\qquad$.
3. 10005 and 10020
3.【Solution】The smallest 5-digit number divisible by 15 is $10005, 10005+15=10020$. According to the operation given in the problem, we only need to take these two five-digit numbers as 10005 and 10020. After 1 operation, the smaller number becomes 15, and the larger number becomes 10005. After several more operations, the smaller number remains unchanged, and the larger number decreases by 15 each time, until the larger number becomes 30. After one more operation, both numbers become 15.