Definition:Septenary Notation

Definition
Septenary notation is the technique of expressing numbers in base $7$.

That is, every number $x \in \R$ is expressed in the form:
 * $\ds x = \sum_{j \mathop \in \Z} r_j 7^j$

where:
 * $\forall j \in \Z: r_j \in \set {0, 1, 2, 3, 4, 5, 6}$