\documentclass{article}
\begin{document}
Brace ``accents'':
$$\newcommand{\demo}[1]{\quad\quad#1{1 \times 2 \times \cdots \times n}\quad\texttt{\string#1}}
\begin{array}{cc}
\demo{\underbrace} & \demo{\overbrace}
\end{array}
$$
\end{document}
