Question 154
Jure wrote positive integers 1 through 2015 on a whiteboard. Urška then inspected the written numbers from smallest to largest respectively and erased each number that was not divisible by 3. From the numbers still left on the whiteboard she then erased from smallest to largest each number that was not divisible by $3^2$. From the remaining numbers she then erased from smallest to largest each number that was not divisible by $3^3$, and so on. Which number did Urška erase last?