Problem:
How many ways are there to color the five vertices of a regular 17-gon either red or blue, such that no two adjacent vertices of the polygon have the same color?
Problem:
How many ways are there to color the five vertices of a regular 17-gon either red or blue, such that no two adjacent vertices of the polygon have the same color?
Solution:
The answer is zero! Call the polygon . Suppose for contradiction such a coloring did exist.
If we color red, then must be blue. From here we find must be red, then must be blue; thus must be red, must be blue. Proceeding in this manner, we eventually find that is red, is blue, and then is red. But and are adjacent and both red, impossible.
The exact same argument holds if we started by coloring blue. Therefore, there are no colorings at all with the desired property.