Main source on Pythagoras and the Pythagoreans:
The Pythagorean Sourcebook and Library, compiled and translated by Kenneth Sylvan Guthrie, introduced and edited by David R. Fideler. Grand Rapids, MI: Phanes Press, 1987.
W.K.C. Guthrie, A History of Greek Philosophy, Vol. 1, The Earlier Presocratics and the Pythagoreans. Cambridge: Cambridge University Press, 1962.
Charles H. Kahn, Pythagoras and the Pythagoreans: A Brief History. Indianapolis, IN: Hackett Publishing, 2001.
Source on the history of the Fifteen Puzzle:
Y. I. Perelman, Fun with Math and Physics. Moscow: Mir Publishers, 1988.
Illustration (Greek coin): Courtesy of the Philosophical Research Society.
Proclus’ quote from Ivor Thomas, Greek Mathematical Works, Vol. I, Thales to Euclid. Great Britain: Fletcher & Son, 1939, p. 155.
Giovanni Belzoni’s book was published in London by John Murray.