<sub>This is in the spirit of the [What is a Word/Phrase™][1] series started by [JLee][2] with **Number** version puzzles.</sub>

---
 
If a number conforms to a special rule, I call it a **BEN Number™**.  
Use the following examples below to find the rule.


$$
% set Title text. (spaces around the text ARE important; do not remove.)
% increase Pad value only if your entries are longer than the title bar.
%
\def\Pad{\P{0.0}}  \def\Title{\textbf{ BEN }}
%
\def\S#1#2{\Space{#1}{20px}{#2px}}\def\P#1{\V{#1em}}\def\V#1{\S{#1}{9}}
\def\T{\Title\textbf{Numbers}^{\;\!™}\Pad}\def\NT{\Pad\textbf{Not}\T\ }\displaystyle
\smash{\lower{29px}\bbox[yellow]{\phantom{\rlap{rubio.2019.05.15}\S{6px}{0}
\begin{array}{cc}\Pad\T&\NT\\\end{array}}}}\atop\def\V#1{\S{#1}{5}}
\begin{array}{|c|c|}\hline\Pad\T&\NT\\\hline
%
\text{  17 }&\text{ 57 }\\ \hline
\text{  24 }&\text{ 64 }\\ \hline
\text{  49 }&\text{ 89 }\\ \hline
\text{  121 }&\text{ 161 }\\ \hline
\text{  158 }&\text{ 198 }\\ \hline
\text{  538 }&\text{ 578 }\\ \hline
\text{  830 }&\text{ 870 }\\ \hline
\text{  1,059 }&\text{ 1,099 }\\ \hline
\text{  1,622 }&\text{ 1,662 }\\ \hline
\text{  2,345 }&\text{ 2,385 }\\ \hline
\end{array}$$


And, if you want to analyze, here is a CSV version:

    BEN Numbers™,Not BEN Numbers™
    17,57
    24,64
    49,89
    121,161
    158,198
    538,578
    830,870
    1059,1099
    1622,1662
    2345,2385

**Bonus Question:**  
It's true that the cardinality of BEN Numbers' set is finite. What is the largest BEN Number?

  [1]: https://puzzling.stackexchange.com/search?q=%22what+is+a%22+word+is%3Aquestion
  [2]: https://puzzling.stackexchange.com/users/463