Polygon with n sides I'm wondering if this is true:
If a polygon with n sides whose vertices are points of integer coordinates and the sides are equal, then n is even.
can you prove or disprove it?

This is a very nice question. The answer to it is given by the paper 
D.G. Ball, "Constructability of regular and equilateral polygons on square pinboards", Mathematical Gazette 57 (1973) p. 119-122.
Theorem. There exists an equilateral lattice $n$-gon in the plane if and only if $n$ is even. Furthermore, if $n$ is even, this polygon can be taken to be convex. 
You can find a proof and much more here. 
Note: A planar polygon is called a lattice polygon if its vertices belong to the usual square lattice on the plane. 
