Definition:Vigesimal System

Definition
The vigesimal system is base $20$ notation.

That is, every number $x \in \R$ is expressed in the form:
 * $\ds x = \sum_{j \mathop \in \Z} r_j 20^j$

where:
 * $\forall j \in \Z: r_j \in \set {0, 1, \ldots, 19}$