\documentclass{article}
\usepackage{amsmath}
\usepackage{caption,tikz}
\usepackage{xepersian}
\settextfont{Yas}
\setdigitfont{Yas}
\begin{document}
\[
G_{D^{-p}f(t)}=\lim _{h \rightarrow 0} h^{p} \sum _{r=0} ^{n} {r \brack p} f(t-rh)
\]
\end{document}