Math 522: Number Theory

Fall 2002
MW, 17:30 - 18:45 am.
San Diego State University

Professor: Mike O'Sullivan
Office: Bus. Adm./Math Building #217, ext. 594-6697
Office Hours: MWF: 13:00-14:00, MW 18:45-19:30.
                             Other times: by appointment or good fortune (I will normally be in my office and available).


Rosen, Elementary Number Theory and Its Applications 4th ed.

Detailed Information

First Maple Worksheet Second Maple Worksheet

Course Description

Number theory is one of the oldest and richest subjects in mathematics. One aspect of the subject that delights mathematicians is that a problem that is very easy to pose can require very difficult and profound mathematical structures to solve. Number theory is also considered to be one of the purest and most beautiful areas of mathematics. Yet in the last few decades it has become an important applied subject as well; for example, the security of internet communications depends on an application of number theory.

We are using an excellent text book in this course. It gives a good introduction to the fundamentals of number theory, includes several practical applications and has interesting discussions of some important unsolved problems and historical topics.

The core material of the course is primes and divisors (Ch. 3) and congruences (Ch. 4, Ch. 6 and parts of Ch. 9). Weaved in with these topics will be several applications of congruences: hashing functions (Sec. 5.4), used by computers to store data; check digits (Sec. 5.5), used for passport and ISBN numbers to protect against typographical erorrs; and cryptography (Secs. 8.4, 10.2), used for internet security.

I hope that you will appreciate the beauty of number theory and acquire a taste for pursuing applications of the subject. I'd like to entice you into the cryptography course (Math 626) offered this Spring or to the new Master of Science program, Mathematical Theory of Communication Systems.


Here is a rough idea of the amount of time I expect to spend on each topic. I am also open to suggestions if the class would like to spend more time on certain topics or cover items not listed here. A day by day schedule (see above) will be maintained to keep you informed of upcoming and past lectures.

§1.1-4 Induction, Fibonacci numbers, divisibility 2 classes
§2.1 Base r representations of integers 2 classes
§3.1-4,6; §13.1-2 Primes, greatest common divisor, Euclidean algorithm. 6 classes
Unique factorization, Diophantine equations.
§4.1-3,5 Congruences, the ring Z/n . 5 classes
Solving linear and quadratic congruences and linear systems.
Chinese remainder theorem.
§5.1,3-5 §8.3, §8.4 Applications: divisibility rules, tournament scheduling, 2 classes
hash functions, check digits,
§6.1, §6.3 Fermat's little theorem, Euler's theorem 2 classes
§8.1-4; §10.2 Cryptography: linear cryptosystems, RSA, El Gamal 3 classes
§7.1-2; §9.1-4 Multiplicative functions: Euler phi, sum and number of divisors. 5 classes
Primitive elements in Z/n .


We will have weekly assignments, two midterms and a final exam. Computer projects (see above) may be done for extra credit up to a total of 100 pts.

Weekly work 350
Test 1 150
Test 2 150
Final 350
Total 1000
For the weekly assignments (see above), there will be a small number of problems (10 or so) which you should write up carefully. I will either collect these and grade them or give a short quiz with some selection of the problems.

For the exams, I will write a list of subject matter and exercises to guide you in your study (link above). These form the material that you are expected to understand upon completion of this course. You can safely ignore material that is not included.

The first exam is tentatively Wed. Oct. 2.

The second exam is tentatively Mon. Nov. 18.

The final is Sat. Dec. 21, 8:00-10:00.