% LaTeX
\documentclass[leqno]{article}
\usepackage[utf8x]{inputenc}
\usepackage{ucs}
\usepackage{url}
\usepackage{braket}
\usepackage{graphicx}
\usepackage[intlimits]{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{bm}
\usepackage{gellmu}
\usepackage[margin=100bp,nohead]{geometry}
\setlength{\parskip}{6bp}
\setlength{\parindent}{0bp}
\pagestyle{plain}
\thispagestyle{empty}
\title{}
\newlength{\centerskip}
\setlength{\centerskip}{\topsep}
\newcommand{\hsf}{\hspace*{\fill}}
\newcommand{\tdbc}[1]{\hsf\textbf{#1}\hsf}
\begin{document}

\medskip
\par{\[ \int_{0}^{\infty{}} \nolimits {t^{x} e^{-t} \frac{d t}{t}} \ \ = \    \ \frac{1}{x} \prod_{k=1}^{\infty{}} {\frac{\left(1 +     \frac{1}{k}\right)^{x}}{\left(1 + \frac{x}{k}\right)} } \]
}
\end{document}

