Published online by Cambridge University Press: 08 March 2016
Let   $\unicode[STIX]{x1D714}=[a_{1},a_{2},\ldots ]$  be the infinite expansion of a continued fraction for an irrational number
 $\unicode[STIX]{x1D714}=[a_{1},a_{2},\ldots ]$  be the infinite expansion of a continued fraction for an irrational number   $\unicode[STIX]{x1D714}\in (0,1)$ , and let
 $\unicode[STIX]{x1D714}\in (0,1)$ , and let   $R_{n}(\unicode[STIX]{x1D714})$  (respectively,
 $R_{n}(\unicode[STIX]{x1D714})$  (respectively,   $R_{n,k}(\unicode[STIX]{x1D714})$ ,
 $R_{n,k}(\unicode[STIX]{x1D714})$ ,   $R_{n,k+}(\unicode[STIX]{x1D714})$ ) be the number of distinct partial quotients, each of which appears at least once (respectively, exactly
 $R_{n,k+}(\unicode[STIX]{x1D714})$ ) be the number of distinct partial quotients, each of which appears at least once (respectively, exactly   $k$  times, at least
 $k$  times, at least   $k$  times) in the sequence
 $k$  times) in the sequence   $a_{1},\ldots ,a_{n}$ . In this paper, it is proved that, for Lebesgue almost all
 $a_{1},\ldots ,a_{n}$ . In this paper, it is proved that, for Lebesgue almost all   $\unicode[STIX]{x1D714}\in (0,1)$  and all
 $\unicode[STIX]{x1D714}\in (0,1)$  and all   $k\geq 1$ ,
 $k\geq 1$ ,  $$\begin{eqnarray}\displaystyle \lim _{n\rightarrow \infty }\frac{R_{n}(\unicode[STIX]{x1D714})}{\sqrt{n}}=\sqrt{\frac{\unicode[STIX]{x1D70B}}{\log 2}},\quad \lim _{n\rightarrow \infty }\frac{R_{n,k}(\unicode[STIX]{x1D714})}{R_{n}(\unicode[STIX]{x1D714})}=\frac{C_{2k}^{k}}{(2k-1)\cdot 4^{k}},\quad \lim _{n\rightarrow \infty }\frac{R_{n,k}(\unicode[STIX]{x1D714})}{R_{n,k+}(\unicode[STIX]{x1D714})}=\frac{1}{2k}.\end{eqnarray}$$
 $$\begin{eqnarray}\displaystyle \lim _{n\rightarrow \infty }\frac{R_{n}(\unicode[STIX]{x1D714})}{\sqrt{n}}=\sqrt{\frac{\unicode[STIX]{x1D70B}}{\log 2}},\quad \lim _{n\rightarrow \infty }\frac{R_{n,k}(\unicode[STIX]{x1D714})}{R_{n}(\unicode[STIX]{x1D714})}=\frac{C_{2k}^{k}}{(2k-1)\cdot 4^{k}},\quad \lim _{n\rightarrow \infty }\frac{R_{n,k}(\unicode[STIX]{x1D714})}{R_{n,k+}(\unicode[STIX]{x1D714})}=\frac{1}{2k}.\end{eqnarray}$$ $R_{n}$  are discussed.
 $R_{n}$  are discussed.