So this is supposedly a very popular puzzle by Sam Loyd. (I don't want answerers to provide solutions directly from some website etc. I mean, an ingenious solution is more welcome please.)
Now, as you see all numbers are arranged in ascending order except the last two. The rule of the game is to move a numbered block which is adjacent to the blank space and create another blank place in its original position (I mean, you just shift the position of blank space around by sliding the numbers around) .
Now the question goes as, can you arrange all the numbers in the correct ascending order? (The final outcome would be just interchange the positions of $15$ and $14$).
I know of a solution using a very clever trick of invariance (the invariant seemed quite non-trivial to me ;-P). Can others here come up with some interesting solutions?