Curved Line Under Number (not sure what it's called)

Question

How would I make something like this in Latex?

Thank you in advance!

Answer 1

You can use the \underbrace command or using mathtools the \underbracket command:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
You can try $1!\underbrace{666\cdots6}{m\textup{ 6's}}$ or $1!\underbracket{666\cdots6}{m\textup{ 6's}}$
\end{document}

If you want a round brace with the text through it, you can use the abraces package (documentation here):

\documentclass{article}
\usepackage{abraces}
\begin{document}
A special underbrace for $1!\aunderbrace[l1@{\raisebox{-2pt}{\smash{\scriptsize,$m$ 6's,}}}1r]{666\cdots6}$.
\end{document}

Or if you want the text lower:

A special underbrace for $1\!\aunderbrace[l1@{\raisebox{-4pt}{\scriptsize\,$m$ 6's\,}}1r]{666\cdots6}$.