1. P. Erdős: Beweis eines Satzes von Tschebyschef, Acta Sci. Math. (Szeged) 5 (1930-32), 194-198.
2. R. L. Graham, D. E. Knuth & O. Patashnik: Concrete Mathematics. A Foundation for Computer Science, Addison-Wesley, Reading MA 1989.
3. G. H. Hardy & E. M. Wright: An Introduction to the Theory of Numbers, fifth edition, Oxford University Press 1979.
4. P. Ribenboim: The New Book of Prime Number Records, Springer-Verlag, New York 1989.