8, 18, 11, 15, 5, 4, 14, 9, 19, 1, 7, 17, 6, 16, ? , ?, ?, ?, ? Now, the only numbers used are in the range of 1 to 19. No numbers can be repeated. Now, there is a pattern to the sequence of numbers, and your keen powers of observation will be able to note that the last five numbers used in the sequence will be some combination of 13, 12, 10, 3, and 2. (If you’re more into logic brain-busters, a MIT professor called this puzzle “the hardest ever.”) Any luck? Here are a few hints: The sequence doesn’t obey any mathematical rule, and it is not counting any particular group of things. The only way to figure out the problem, according to Spencer, is to think of the numbers as words and write them out. The completed sequence is as follows: 8, 18, 11, 15, 5, 4, 14, 9, 19, 1, 7, 17, 6, 16, 10, 13, 3, 12, 2. Numerically, the sequence’s order is meaningless. That’s because they’re actually just listed in alphabetical order. While you’re in puzzle-mode, a bunch of raccoons solved this ancient Greek riddle—can you figure it out?