The * Disquisitiones Arithmeticae* (
Latin for "Arithmetical Investigations") is a textbook of
number theory written in Latin by
Carl Friedrich Gauss in 1798 when Gauss was 21 and first published in 1801 when he was 24. It is notable for having had a revolutionary impact on the field of number theory as it not only made the field truly rigorous and systematic but also paved the path for modern number theory. In this book Gauss brought together and reconciled results in number theory obtained by mathematicians such as
Fermat,
Euler,
Lagrange, and
Legendre and added many profound and original results of his own.

The *Disquisitiones* covers both
elementary number theory and parts of the area of mathematics now called
algebraic number theory. Gauss did not explicitly recognize the concept of a
group, which is central to
modern algebra, so he did not use this term. His own title for his subject was Higher Arithmetic. In his Preface to the *Disquisitiones*, Gauss describes the scope of the book as follows:

The inquiries which this volume will investigate pertain to that part of Mathematics which concerns itself with integers.

Gauss also writes, "When confronting many difficult problems, derivations have been suppressed for the sake of brevity when readers refer to this work." ("Quod, in pluribus quaestionibus difficilibus, demonstrationibus syntheticis usus sum, analysinque per quam erutae sunt suppressi, imprimis brevitatis studio tribuendum est, cui quantum fieri poterat consulere oportebat")

The book is divided into seven sections:

- Congruent Numbers in General
- Congruences of the First Degree
- Residues of Powers
- Congruences of the Second Degree
- Forms and Indeterminate Equations of the Second Degree
- Various Applications of the Preceding Discussions
- Equations Defining Sections of a Circle

These sections are subdivided into 366 numbered items, which state a theorem with proof or otherwise develop a remark or thought.

Sections I to III are essentially a review of previous results, including Fermat's little theorem, Wilson's theorem and the existence of primitive roots. Although few of the results in these sections are original, Gauss was the first mathematician to bring this material together in a systematic way. He also realized the importance of the property of unique factorization (assured by the fundamental theorem of arithmetic, first studied by Euclid), which he restates and proves using modern tools.

From Section IV onward, much of the work is original. Section IV develops a proof of quadratic reciprocity; Section V, which takes up over half of the book, is a comprehensive analysis of binary and ternary quadratic forms. Section VI includes two different primality tests. Finally, Section VII is an analysis of cyclotomic polynomials, which concludes by giving the criteria that determine which regular polygons are constructible, i.e., can be constructed with a compass and unmarked straightedge alone.

Gauss started to write an eighth section on higher-order congruences, but did not complete it, and it was published separately after his death with the title *Disquisitiones generales de congruentiis* (Latin: 'General Investigations on Congruences').^{
[1]} In it Gauss discussed congruences of arbitrary degree, attacking the problem of general congruences from a standpoint closely related to that taken later by
Dedekind,
Galois, and
Emil Artin. The treatise paved the way for the theory of function fields over a
finite field of constants. Ideas unique to that treatise are clear recognition of the importance of the
Frobenius morphism, and a version of
Hensel's lemma.

The *Disquisitiones* was one of the last mathematical works written in scholarly
Latin. An English translation was not published until 1965.

Before the *Disquisitiones* was published, number theory consisted of a collection of isolated theorems and conjectures. Gauss brought the work of his predecessors together with his own original work into a systematic framework, filled in gaps, corrected unsound proofs, and extended the subject in numerous ways.

The logical structure of the *Disquisitiones* (
theorem statement followed by
proof, followed by
corollaries) set a standard for later texts. While recognising the primary importance of logical proof, Gauss also illustrates many theorems with numerical examples.

The *Disquisitiones* was the starting point for other 19th-century European mathematicians, including
Ernst Kummer,
Peter Gustav Lejeune Dirichlet and
Richard Dedekind. Many of Gauss's annotations are in effect announcements of further research of his own, some of which remained unpublished. They must have appeared particularly cryptic to his contemporaries; they can now be read as containing the germs of the theories of
L-functions and
complex multiplication, in particular.

The *Disquisitiones* continued to exert influence in the 20th century. For example, in section V, article 303, Gauss summarized his calculations of
class numbers of proper primitive binary quadratic forms, and conjectured that he had found all of them with class numbers 1, 2, and 3. This was later interpreted as the determination of imaginary quadratic number fields with even discriminant and class number 1, 2, and 3, and extended to the case of odd discriminant. Sometimes called the
class number problem, this more general question was eventually confirmed in 1986^{
[2]} (the specific question Gauss asked was confirmed by
Landau in 1902^{
[3]} for class number one). In section VII, article 358, Gauss proved what can be interpreted as the first nontrivial case of the
Riemann hypothesis for curves over finite fields (the
Hasse–Weil theorem).^{
[4]}

- Carl Friedrich Gauss, tr. Arthur A. Clarke,
^{ [5]}S.J.:*Disquisitiones Arithmeticae*, Yale University Press, 1965, ISBN 0-300-09473-6 -
*Disquisitiones Arithmeticae*(original text in Latin) - Dunnington, G. Waldo (1935), "Gauss, His Disquisitiones Arithmeticae, and His Contemporaries in the Institut de France",
*National Mathematics Magazine*,**9**(7): 187–192, doi: 10.2307/3028190, JSTOR 3028190

**^*** Latin text, with endnotes by Dedekind: Gauss, Carl Friedrich (1863).*Disquisitiones generales de congruentiis*.*Carl Friedrich Gauss Werke*. Vol. Band II. Königlichen Gesellschaft der Wissenschaften zu Göttingen. pp. 212–242.- Translated into German: Gauss, Carl Friedrich (1889).
*Allgemeine Untersuchungen über die Congruenzen*.*Carl Friedrich Gauss’ Untersuchungen über höhere Arithmetik*. Translated by Maser, Hermann. Berlin: Julius Springer. pp. 602–629.

- Translated into German: Gauss, Carl Friedrich (1889).
**^**Ireland, K.; Rosen, M. (1993),*A Classical Introduction to Modern Number Theory*, New York, New York: Springer-Verlag, pp. 358–361, ISBN 978-0-387-97329-6**^**Goldfeld, Dorian (July 1985), "Gauss' Class Number Problem For Imaginary Quadratic Fields" (PDF),*Bulletin of the American Mathematical Society*,**13**(1): 23–37, doi: 10.1090/S0273-0979-1985-15352-2**^**Silverman, J.; Tate, J. (1992),*Rational Points on Elliptic Curves*, New York, New York: Springer-Verlag, p. 110, ISBN 978-0-387-97825-3**^**Not to be confused with Arthur C. Clarke, the science fiction author.

- Media related to Disquisitiones Arithmeticae at Wikimedia Commons
- Latin Wikisource has original text related to this article: Disquisitiones arithmeticae (Latin original) (first ed. 1801) (ed. 1870)
- French Wikisource has original text related to this article: Recherches arithmétiques (French translation) (ed. 1807)