\documentclass[a4paper,12pt]{article}
\usepackage{amsmath}
\usepackage[plainpages=false,colorlinks,pagebackref=true,citecolor=blue]{hyperref}

\usepackage{xepersian}

\settextfont[Scale=1]{XB Zar}
%\setlatintextfont[Scale=1]{Times New Roman}
\setdigitfont{Yas}%{XB Zar}

\DeclareMathSizes{12}{100}{30}{10} %{10.95}{9.2}{7.3}{5.5}%12,10,8,6

\begin{document}
\begin{align}
E = mc^2\\
\sum_{i=1}^{n_1}x_{j_i}
\end{align}
\end{document}