For every polyhedron the number $V$ of its vertices plus the number $F$ of its faces minus the number $E$ of its edges is equal to 2:

$$V+F-E=2.\label{*}\tag{*}$$

Euler's theorem hold for polyhedrons of genus $0$; for polyhedrons of genus $p$ the relation

$$V+F-E=2-2p$$

holds. This theorem was proved by L. Euler (1758); the relation \eqref{*} was known to R. Descartes (1620).