  A general setting for nested subdivisions of a bounded real set into
intervals defining the digits $X_1,X_2,...$ of a random variable $X$ with a
probability density function $f$ is considered. Under the weak condition that
$f$ is almost everywhere lower semi-continuous, a coupling between $X$ and a
non-negative integer-valued random variable $N$ is established so that
$X_1,...,X_N$ have an interpretation as the ``sufficient digits'', since the
distribution of $R=(X_{N+1},X_{N+2},...)$ conditioned on $S=(X_1,...,X_N)$ does
not depend on $f$. Adding a condition about a Markovian structure of the
lengths of the intervals in the nested subdivisions, $R\,|\,S$ becomes a Markov
chain of a certain order $s\ge0$. If $s=0$ then $X_{N+1},X_{N+2},...$ are IID
with a known distribution. When $s>0$ and the Markov chain is uniformly
geometric ergodic, a coupling is established between $(X,N)$ and a random time
$M$ so that the chain after time $\max\{N,s\}+M-s$ is stationary and $M$
follows a simple known distribution. The results are related to several
examples of number representations generated by a dynamical system, including
base-$q$ expansions, generalized L\"uroth series, $\beta$-expansions, and
continued fraction representations. The importance of the results and some
suggestions and open problems for future research are discussed.
