A strange symbol-where can I find it?

Question

Please, in which LaTeX package can I find the symbol between $s$ and $\langle n\rangle$ below ?

Answer 1

Probably you are asking for the first one in the example below (\frown). The second one is a variant provided by amssymb (\smallfrown).

\documentclass{article}
\usepackage{amssymb}
\begin{document}
$s \frown \langle n\rangle$
$s \smallfrown \langle n\rangle$
\end{document}