%% 
%%  Der Mathematiksatz mit LaTeX, 1. Auflage 2009
%% 
%%  Example 8-2-7 on page 166.
%% 
%%  Copyright (C) 2009 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.
%% 

\documentclass[]{ttctminimal}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{122.59192pt}
\usepackage[utf8]{inputenc}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
\mathchardef\Sum="1358 % großes Summenzeichen
$a\Sum\limits_{i=1}^{\infty}\sqrt{i+1}$\\[10pt]
$a\sum\limits_{i=1}^{\infty}\sqrt{i+1}$
\end{document}