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
Jonathan Borwein
Christian Boyer
Peter Dinkelacker
Andreas Fillipi
Dirk Frettlöh
Erich Friedman
Heiko Harborth

Michael Joswig
Bernhard Klaaßen
Sascha Kurz
Jeffrey Lagarias
William McEachen
Lee Morgenstern
Tony Noe
Wulf Rehder

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