# Euler characteristic

The Euler characteristic is one of the important quantities, known as a **topological invariant**,
that describes the shape or structure of topological
space. Leonhard Euler originally formulated
the characteristic for polyhedra and used it to prove various theorems about
them, including the classification of the Platonic
solids. For the special case of polyhedra, the Euler characteristic
equals 2 (see Euler's formula
for polyhedra).

In algebraic topology, the Euler characteristic arises from homology and connects to many other invariants.