AoPS Wiki talk:Problem of the Day/June 6, 2011

Solution

Just rewrite the numbers over and over and get rid of every 9th:

1 2 3 4 5 6 7 8 9 Remove the 9

10 11 12 1 2 3 4 5 6 Remove the 6

7 8 10 11 12 1 2 3 4 Remove the 4

5 7 8 10 11 12 1 2 3 Remove the 3

5 7 8 10 11 12 1 2 5 Remove the 5

7 8 10 11 12 1 2 7 8 Remove the 8

10 11 12 1 2 7 10 11 12 Remove the 12

10 11 1 2 7 10 11 1 2 Remove the 2

7 10 11 1 7 10 11 1 7 Remove the 7

10 11 1 10 11 1 10 11 1 Remove the 1

10 11 10 11 10 11 10 11 10 Remove the 10

The last number to be destroyed is .