Euler Characteristic

For any convex polyhedron: V - E + F = 2. This quantity is a topological invariant.

V = 4 − E = 6 + F = 4 = 2

Sphere (genus 0): X = 2

Torus (genus 1): X = 0

Double torus (genus 2): X = -2

Formula: X = 2 - 2g