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Taking a base $z$ positional numeral system with digits $a_i\in \{0,\ldots,n-1\}$:
$$s:\left\{(a_i)\in\{0,\ldots,n-1\}^{\mathbb{Z}}: \exists_N \forall_{i>N} \ a_i=0\right \}\to \sum_{i\in\mathbb{Z}} a_i z^i $$
we usually take $z=n$ (or $z=-n$), making $s$ "nearly bijection" with $\mathbb{R}^+...