Math 567 -- Elementary Number Theory

MATH 567

Elementary Number Theory

MWF 1:20-2:10, Van Vleck B119 Professor: Jordan Ellenberg (ellenber@math.wisc.edu) Office Hours: Weds, 2:30-3:30, Van Vleck 323.

Grader: Silas Johnson (sjohnson@math.wisc.edu)

Math 567 is a course in elementary number theory, aimed at undergraduates majoring in math or other quantitative disciplines. A general familiarity with abstract algebra at the level of Math 541 will be assumed, but students who haven't taken 541 are welcome to attend if they're willing to play a little catchup. We will be using William Stein's new (and cheap) textbook Elementary Number Theory: Primes, Congruences, and Secrets, which emphasizes computational approaches to the subject. If you don't need a physical copy of the book, it is available as a free legal .pdf. We will be using the (free, public-domain) mathematical software SAGE, developed largely by Stein, as an integral component of our coursework.

Topics include some subset of, but are not limited to: Divisibility, the Euclidean algorithm and the GCD, linear Diophantine equations, prime numbers and uniqueness of factorization. Congruences, Chinese remainder theorem, Fermat's "little" theorem, Wilson's theorem, Euler's theorem and totient function, the RSA cryptosystem. Number-theoretic functions, multiplicative functions, Möbius inversion. Primitive roots and indices. Quadratic reciprocity and the Legendre symbol. Perfect numbers, Mersenne primes, Fermat primes. Pythagorean triples, Special cases of Fermat's "last" theorem. Fibonacci numbers. Continued fractions. Distribution of primes, discussion of prime number theorem. Primality testing and factoring algorithms.

Course Policies: Homework will be due on Fridays. It can be turned in late only with advance permission from your grader. It is acceptable to use calculators and computers on homework (indeed, some of it will require a computer) but calculators are not allowed during exams. You are encouraged to work together on homework, but writeups must be done individually.

Grading: The grade in Math 567 will be composed of 40% homework, 20% each of three midterms. The last midterm will be take-home, and will be due on the last day of class. There will be no final exam in Math 567.

Syllabus: (This may change as we see what pace works well for the course. All section numbers refer to Stein's book.)

• Sep 3-10: Prime numbers, prime factorizations, Euclidean algorithm and GCD (1.1-1.3)
• Sep 13-17: The integers mod n, Euler's theorem, the phi function (2.1-2.2)
• Sep 20-24: Modular exponentiation, primality testing, and primitive roots (2.4-2.5)
• Sep 27-Oct 1: Public-key cryptography and RSA (3.1-3.4)
• Oct 4 - 8: Algebraic numbers
• Oct 8: First midterm exam
• Oct 11-15: Quadratic reciprocity (4.1-4.4)
• Oct 18-22: Finite and infinite continued fractions (5.1-5.3)
• Oct 25-29: Continued fractions and diophantine approximation (5.4-5.5)
• Nov 1-5: Diophantine equations I: Pell's equation and Lagrange's theorem
• Nov 8-12: Elliptic curves (6.1-6.2)
• Nov 15-19: Applications of elliptic curves (6.3-6.4)
• Nov 22-Dec 3: Diophantine equations II: Fermat, generalized Fermat, and probabilistic methods
• Dec 6-15: advanced topic TBD: maybe a look at the Sato-Tate conjecture?

Homework:

• Sep 10: