Euler’s Formula

Euler’s Formula says: for any convex polyhedron (which includes the five Platonic Solids) the Number of Faces plus the Number of Vertices (corner points) minus the Number of Edges always equals 2
 It is written: F + V – E = 2

Try it on the cube:

A cube has 6 Faces, 8 Vertices, and 12 Edges,

so:

6 + 8 – 12 = 2

Source: http://www.mathsisfun.com/geometry/platonic-solids-why-five.html