Vorlesungen über Zahlentheorie
Vorlesungen über Zahlentheorie (German for Lectures on Number Theory) is a textbook of number theory written by German mathematicians Peter Gustav Lejeune Dirichlet and Richard Dedekind, and published in 1863.
Based on Dirichlet's number theory course at the University of Göttingen, the Vorlesungen were edited by Dedekind and published after Lejeune Dirichlet's death. Dedekind added several appendices to the Vorlesungen, in which he collected further results of Lejeune Dirichlet's and also developed his own original mathematical ideas.
The Vorlesungen cover topics in elementary number theory, algebraic number theory and analytic number theory, including modular arithmetic, quadratic congruences, quadratic reciprocity and binary quadratic forms.
The contents of Professor John Stillwell's 1999 translation of the Vorlesungen are as follows
- Chapter 1. On the divisibility of numbers
- Chapter 2. On the congruence of numbers
- Chapter 3. On quadratic residues
- Chapter 4. On quadratic forms
- Chapter 5. Determination of the class number of binary quadratic forms
- Supplement I. Some theorems from Gauss's theory of circle division
- Supplement II. On the limiting value of an infinite series
- Supplement III. A geometric theorem
- Supplement IV. Genera of quadratic forms
- Supplement V. Power residues for composite moduli
- Supplement VI. Primes in arithmetic progressions
- Supplement VII. Some theorems from the theory of circle division
- Supplement VIII. On the Pell equation
- Supplement IX. Convergence and continuity of some infinite series
This translation does not include Dedekind's Supplements X and XI in which he begins to develop the theory of ideals.
The German titles of supplements X and XI are:
- Supplement X: Über die Composition der binären quadratische Formen,
- Supplement XI: Über die Theorie der ganzen algebraischen Zahlen.
Chapters 1 to 4 cover similar ground to Gauss' Disquisitiones Arithmeticae, and Dedekind added footnotes which specifically cross-reference the relevant sections of the Disquisitiones. These chapters can be thought of as a summary of existing knowledge, although Dirichlet simplifies Gauss' presentation, and introduces his own proofs in some places.
Chapter 5 contains Dirichlet's derivation of the class number formula for real and imaginary quadratic fields. Although other mathematicians had conjectured similar formulae, Dirichlet gave the first rigorous proof.
Supplement VI contains Dirichlet's proof that an arithmetic progression of the form a+nd where a and d are coprime contains an infinite number of primes.
The Vorlesungen can be seen as a watershed between the classical number theory of Fermat, Jacobi and Gauss, and the modern number theory of Dedekind, Riemann and Hilbert. Dirichlet does not explicitly recognise the concept of the group that is central to modern algebra, but many of his proofs show an implicit understanding of group theory.
The Vorlesungen contains two key results in number theory which were first proved by Dirichlet. The first of these is the class number formulae for binary quadratic forms. The second is a proof that arithmetic progressions contains an infinite number of primes (known as Dirichlet's theorem); this proof introduces Dirichlet L-series. These results are important milestones in the development of analytic number theory.
- These translate as "On the composition of binary quadratic forms" and "On the theory of algebraic integers", respectively.
- P. G. Lejeune Dirichlet, R. Dedekind tr. John Stillwell: Lectures on Number Theory, American Mathematical Society, 1999 ISBN 0-8218-2017-6
- Note that the Göttinger Digitalisierungszentrum has a scanned copy of the original, 2nd edition text (in German) published in 1871 containing supplements I–X.
- Supplement XI can be found in volume three of Dedekind's complete works also at the Göttinger Digitalisierungszentrum.
- The 4th edition from 1894 which contains all of the supplements including Dedekind's XI is available at Internet Archive.