Euler's Polygon Division Problem

The problem of finding in how many ways $E_n$ a Plane convex Polygon of $n$ sides can be divided into Triangles by diagonals. Euler first proposed it to Christian Goldbach in 1751, and the solution is the Catalan Number $E_n=C_{n-2}$.

See also Catalan Number, Catalan's Problem

References

Guy, R. K. ``Dissecting a Polygon Into Triangles.'' Bull. Malayan Math. Soc. 5, 57-60, 1958.