A nice new mathematical puzzles competition (in French) is open until 16 May: “Mathematics on a shelf“, a collection of 19 puzzles. Many are quite classical and all can be solved by high school students. The hardest is probably the 11th: create a puzzle, the solution of which must be 2718. The most elegant puzzle wins.
The most obvious property of 2718 is that it is the floor of , but that doesn’t make an elegant puzzle yet!