%% 
%%  An UIT Edition example
%% 
%%  Example 10-06-4 on page 212.
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{352.81416pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
The Euclidean algorithm: if $a>b$ are integers then $\gcd(a,b)=\gcd(a\bmod b,b)$.
If $\prod_{i=1}^n p^{e_i}_i$ is the prime factorization of $x$ then
\[
  S(x)=\sum_{d\vert x}d=\prod_{i=1}^n{p^{e_i+1}_i-1\over p_i-1}.
\]
\end{document}