Prof. Dr. Jochen Ziegenbalg 

In addition to the material on my German (primary) homepage, here is some material in English.

Curriculum Vitae in English 
Some internet based materials in English   
   
  Interactive experiments and simulations
   
  Computeralgebra notebooks in Mathematica 
(More notebooks in German can be found on my German homepage.) 
    1. Mathematical Modelling, Dynamic Processes and Difference Equations
   

1.1 Introduction
1.2 Cobweb Diagrams 
1.3 Closed Form Representation  

   
   

2. Mean values      
   
2.1 Pythagorean Means
    3. Elementary Number Theory, Applications and Visualisation
   

3.1 Phi, Tau, Sigma in Elementary Number Theory   
3.2 Figurate Numbers 
Computeralgebra notebooks in Maxima 
The following Maxima notebooks (or "worksheets") are stored in a "raw" ASCII format.  They can be downloaded and should be opened using the Open Source Maxima computeralgebra system (CAS)  -  in  the wxMaxima-version.  Thus, i.e. in the Maxima "frontend" form, they look much more pleasant - and the notebook functions or programs can be executed interactively.  
Download site for Maxima e.g.:  http://maxima.sourceforge.net/  
In some browsers, depending on various system configuration parameters the files are displayed in the wxMaxima "frontend" form without further ado.  Necessary (but by no means sufficient) for this to happen is, of course, that the Maxima computeralgebra system is installed on the computer and that the file suffix "wxm" is properly linked to the application program (i.e. Maxima).    
1.  Some historical algorithms
2.  Modeling and Simulation