\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
>···1+1=2\\
>···2+2=4\tag{2}\label{eqn:2}\\
>···4+4=8\\
\end{align*}

Note that \eqref{eqn:2} is comparable to $2*2=4$
\end{document}