\documentclass[12pt]{article} \pagestyle{empty} \begin{document} \begin{displaymath} p_{\rm trial}^{\rm arb}(r) = {{1}\over{n_{\rm finite}}} \end{displaymath} \end{document}
\documentclass[12pt]{article} \pagestyle{empty} \begin{document} \begin{displaymath} p_{\rm trial}^{\rm arb}(r) = {{1}\over{n_{\rm finite}}} \end{displaymath} \end{document}