My greatest thanks go to my mathematics teacher Dr. Franz Hagen, who accompanied me from the 9th grade to the Abitur (final high-school examination) at the Gymnasium Oer-Erkenschwick (high-school). He was the one who gave me the joy of mathematics and recognized something like a talent. I dedicate this website to him.

I thank the many colleagues all over the world who were so kind to answer my questions, to criticize my texts and ideas constructively or to help me in other ways. Furthermore, I would like to mention the following people in alphabetical order.

Friedrich Ludwig Bauer
Christian Boyer
Jonathan Borwein
Lev Bukovsky
Peter Dinkelacker
Andreas Fillipi
Erich Friedman
Dirk Frettlöh
Heiko Harborth

Erhard Hexel
Michael Joswig
Bernhard Klaaßen
Sascha Kurz
Jeffrey Lagarias
Lee Morgenstern
Tony Noe
Christoph Pöppe
Roman Soták

Wulf Rehder
Harald Scheid
David Sixsmith
Neil Sloane
Alexander Soifer
Stefan Vogel
Hans Walser
Günther Wirsching
Dieter Wolke