We are interested in tiling a rectangle with copies of single tile (rotations and reflexions are allowed). This is very easy to do, by cutting the rectangle into smaller rectangles.

What happens when we ask the pieces not to be rectangular?

For an even number of pieces, this is easy again (cut it into rectangles, and then cut every rectangle in two through its diagonal. Other tilings are also easy to find).

The interesting (and difficult) case is tiling with an **odd** number of **non-rectangular** pieces.

Some questions:

- Can you give examples of such tilings?
- What is the smallest (odd) number of pieces for which it is possible?
- Is it possible for every number of pieces? (
*e.g.*, with five)

There are two main versions of the problem: the polyomino case (when the tiles are made of unit squares), and the general case (when the tiles can have any shape). The answers to the above questions might be different in each case.

It seems that it is impossible to do with three pieces (I have some kind of proof), and the smallest number of pieces I could get is $15$, as shown above:

This problem is very useful for spending time when attending some boring talk, etc.