\(\RNrSpc{3}\) has three basic coordinate vectors.
In the physics literature these are often written as
\(\mathbf{i}\DefEq \mathbf{e}_1,\qquad \mathbf{j}\DefEq \mathbf{e}_2,\quad \text{and}\quad \mathbf{k}\DefEq \mathbf{e}_3\)
\(\RNrSpc{4}\) has four basic coordinate vectors