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This book tells the story of irrational numbers from their discovery in the days of Pythagoras to the ideas behind the work of Baker and Mahler on transcendence in the 20th century. It focuses on themes of irrationality, algebraic and transcendental numbers, continued fractions, approximation of real numbers by rationals, and relations between automata and transcendence. This book serves as a guide and introduction to number theory for advanced undergraduates and early postgraduates. The book includes a wide range of exercises, from routine problems to surprising and thought-provoking extension material.

**1. Introduction.** 1.1. Irrational Surds. 1.2. Irrational Decimals. 1.3. Irrationality of the Exponential Constant. 1.4. Other Results, and Some Open Questions. Exercises. Appendix: Some Elementary Number Theory. **2. Hermite’s Method.** 2.1. Irrationality of *e ^{r}. *2.2. Irrationality of

*π.*2.3. Irrational values of trigonometric functions. Exercises. Appendix: Some Results of Elementary Calculus.

**3. Algebraic & Transcendental Numbers.**3.1. Definitions and Basic Properties. 3.2. Existence of Transcendental Numbers. 3.3. Approximation of Real Numbers by Rationals. 3.4. Irrationality of (3) : a sketch. Exercises. Appendix 1: Countable and Uncountable Sets. Appendix 2: The Mean Value Theorem. Appendix 3: The Prime Number Theorem.

**4. Continued Fractions.**Definition and Basic Properties. 4.2. Continued Fractions of Irrational Numbers. 4.3. Approximation Properties of Convergents. 4.4. Two important Approximation Problems. 4.5. A "Computational" Test for Rationality. 4.6. Further Approximation Properties of Convergents. 4.7. Computing the Continued Fraction of an Algebraic Irrational. 4.8. The Continued Fraction of

*e.*Exercises. Appendix 1: A Property of Positive Fractions. Appendix 2: Simultaneous Equations with Integral Coefficients. Appendix 3: Cardinality of Sets of Sequences. Appendix 4: Basic Musical Terminology.

**5. Hermite’s Method for Transcendence.**5.1. Transcendence of

*e.*5.2. Transcendence of

*π. 5.3.*Some more Irrationality Proofs. 5.4. Transcendence of e

^{a }.5.5. Other Results. Exercises. Appendix 1: Roots and Coefficients of Polynomials. Appendix 2: Some Real and Complex Analysis. Appendix 3: Ordering Complex Numbers.

**6. Automata and Transcendence.**6.1. Deterministic Finite Automata. 6.2 Mahler’s Transcendence Proof. 6.3 A More General Transcendence Result. 6.4. A Transcendence Proof for the Thue Sequence. 6.5. Automata and Functional Equations. 6.6. Conclusion. Exercises. Appendix 1: Alphabets, Languages and DFAs. Appendix 2: Some Results of Complex Analysis. Appendix 3: A Result on Linear Equations.

**7. Lambert’s Irrationality Proofs.**7.1. Generalised Continued Fractions. 7.2. Further Continued Fractions. Exercises. Appendix: Some Results from Elementary Algebra and Calculus. Hints for Exercises. Bibliography. Index.

### Biography

**David Angell** studied mathematics at Monash University and the University of New South Wales, Australia, earning a Ph.D. from the latter institution with a thesis on Mahler’s method in transcendence theory. He has been a member of the academic staff in the School of Mathematics at UNSW since 1989, and has consistently received glowing evaluations of his teaching both from colleagues and from students. David has taught a wide variety of mathematics subjects, but his favourites have always been number theory and discrete mathematics. He is particularly interested in teaching students to produce proofs and other mathematical writing which are clearly expressed, logically impeccable and engaging for the reader. David is strongly committed to extension activities for secondary school students. He has for many years been the problems editor for *Parabola*, the online mathematics magazine produced by UNSW, as well as contributing a number of articles to the magazine. He has also given talks on a wide variety of topics to final-year secondary students.

Beyond mathematics, David is an enthusiast for wilderness activities and has undertaken expeditions in Australia, Greenland, Nepal, Morocco and many other areas. He is a keen amateur musician, and is the founding conductor of the Bourbaki Ensemble, a chamber string orchestra based in Sydney, Australia.

"Exceptionally informative, impressively organized and presented,

Irrationality and Transcendence in Number Theoryis an ideal selection as a curriculum textbook."-Midwest Books Review

"This excellent book not only helps fill a substantial gap in the undergraduate mathematics literature, but it does so in a way that most students will, I think, find interesting, inviting and accessible.

[. . .] This material is, of course, very nontrivial, but Angell goes to great lengths to make it accessible. He writes slowly and clearly and spends a lot of time motivating results. As previously noted, he also includes background Appendices in each chapter.

There are other useful pedagogical features. Each chapter ends with an extensive collection of exercises, most of them non-routine; a 20-page section at the end of the book offers hints to these. The book also contains a five-page bibliography (one that, surprisingly, omits the Burger/Tubbs book mentioned earlier) that directs a reader to useful sources.

The subject matter of this book is interesting and beautiful and deserves to be made accessible to well-prepared senior undergraduates. Angell has done an excellent job in helping to do so."-MAA Reviews