\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}

\thispagestyle{empty}
\begin{document}
\begin{equation}
  y=N_{0,1}e^{-\frac{(x-x_{0,1})^2}{2\sigma_1^2}}+N_{0,2}e^{-\frac{(x-x_{0,2})^2}{2\sigma_2^2}}\notag
\end{equation}
\end{document}
