The plane is divided into equilateral triangles of side length 1. Consider a equilateral triangle of side length n whose sides lie on the grid lines. On every grid point on the edge and inside of this triangle lies a stone. In a move, a unit triangle is selected, which has exactly 2 corners with is covered with a stone. The two stones are removed, and the third corner is turned a new stone was laid. For which n is it possible that after finitely many moves only one stone left? combinatoricscombinatorial geometry