Definition:Geometric Sequence

A geometric progression is a sequence $$\left \langle{x_n}\right \rangle$$ in $$\R$$ defined as:
 * $$x_n = a r^{n-1}$$ for $$n = 1, 2, 3, \ldots$$

where:
 * $$r \in \R: r \ne 0$$ is called the common ratio;
 * $$a \in \R: a \ne 0$$ is called the scale factor.

Thus its general form is:
 * $$a, ar, ar^2, ar^3, \ldots$$