Quantitative Reasoning 28

The Magic of Numbers

Catalog description

This course will explore the beauty and mystery of mathematics through a study of the patterns and properties of the natural numbers 1,2,3... . We'll discuss various special classes of numbers, like Fibonacci numbers, factorials and binomials and the many ways they arise in mathematics and nature. We'll also investigate the mysterious behavior of the prime numbers and their distribution, and alternative counting systems such as modular arithmetic.

Prerequisites

We will assume no mathematical background beyond high school algebra. Emphasis will be placed on discovery through conjecture and experimentation.

Faculty

NameOfficeE-mail address
Noam ElkiesScience Center 335 elkies@math.harvard.edu
Barry MazurScience Center 512 mazur@math.harvard.edu

Teaching Fellows

NameOfficeE-mail address
Grigor GrigorovScience Center 431h grigorov@math.harvard.edu
Florian HerzigScience Center 431e herzig@math.harvard.edu
Robert NeelScience Center 428d rwneel@math.harvard.edu

Course Website

www.courses.fas.harvard.edu/~qr28

Course Texts

Benedict Gross and Joseph Harris, The Magic of Numbers.

The course text is available for purchase at the Coop.

Homework

There will be short homework assignments after each lecture. The homework will be designed to review concepts from the previous lecture, to reinforce topics in the reading and to introduce some of the ideas of the next lecture. Grades for the homework will be as follows: check-plus for outstanding work; check for good work; check-minus for satisfactory work; minus for unsatisfactory or no work. All of the homework questions will be posted on the course's website; they will not be handed out in class. Homework is due the lecture after it is assigned. Absolutely no late homework will be accepted, but the lowest three homework grades will be discarded at the end of the semester.

Exams

There will be two midterm examinations during the semester and a final exam during finals period. The midterms will be given during class on Wednesday, March 2nd and Wednesday, April 13th. If you have a conflict with either of the exam times, notify one of the TF's immediately. The final exam is scheduled for Wednesday, May 25 and is administered by the registrar's office.

Grading Policy

The final grade will be based on the homework, the two midterms, and the final. The homework and each midterm will count for 20% of the final grade, and the final exam will count for 40% of the final grade. Minor adjustments may be made to take into account improvement during the semester.

Sections

Section times will be announced in the second week of the course, based upon the students' schedules. These will meet for one hour per week. In section we will review some topics from lecture and explore related issues. Section attendance is required. We will ask you on Monday, February 7th, for the openings in your schedules and we will e-mail your section assignments to you once they are available. Sections will begin meeting during the second week of classes.

Schedule

Below is the tentative lecture schedule for the course. It may change somewhat depending on the length of time required for certain topics and student interest.

Wednesday, February 2: The Remarkable Fibonacci Numbers

Arithmetic and geometric progressions; patterns among Fibonacci numbers; examples in nature.

Friday, February 4: How to Count Without Counting I

Counting problems; counting numbers.

Gross-Harris, Chapter 1

Monday, February 7: How to Count Without Counting II

The multiplication principle, and factorials.

Gross-Harris, Chapter 2

Wednesday, February 9: How to Count Without Counting III

More counting: Inclusion/Exclusion, and the Subtraction Principle.

Gross-Harris, Chapter 3

Friday, February 11: Counting Collections of Objects

Binomial and multinomial coefficients; more examples.

Gross-Harris, Chapter 4

Monday, February 14: Probability

The notion of probability; combinatorial examples; mathematical interpretations of coin problems, dice, and card games.

Gross-Harris, Chapter 5

Wednesday, February 16: Pascal's Triangle

Patterns among binomial coefficients; Pascal's triangle; the binomial theorem.

Gross-Harris, Chapter 6

Friday, February 18: Finish and Recap Counting and Probability

Monday, February 21: President's Day (no class)

Wednesday, February 23: The Euclidean Algorithm

Divisibility; greatest common divisors; Euclid's algorithm.

Gross-Harris, Chapter 8

Friday, February 25: The Euclidean Algorithm II

Divisibility; greatest common divisors; Euclid's algorithm.

Gross-Harris, Chapter 8

Monday, February 28: Review

Wednesday, March 2: First Midterm Exam

Friday, March 4: Diophantine Equations I

Combinations and linear diophantine equations (solving equations with whole numbers).

Gross-Harris, Sections 9.1-9.2

Monday, March 7: Diophantine Equations II

Explicit solutions to linear diophantine equations via the Euclidean algorithm.

Gross-Harris, Sections 9.3-9.4

Wednesday, March 9: Prime Numbers

Prime and composite numbers; existence of infinitely many primes; sieve of Eratosthenes.

Gross-Harris, Chapter 10

Friday, March 11: Unique Factorization

Statement of unique factorization; examples of non-unique factorization.

Gross-Harris, Chapter 11

Monday, March 14: Consequences of Unique Factorization

Greatest common divisors and least common multiples; relative primeness; number of factors of integers.

Gross-Harris, Chapter 12 and Section 13.1

Wednesday, March 16: Numbers and Number Systems

Natural numbers; integers; rational numbers; real numbers.

Gross-Harris, Chapter 14

Friday, March 18: Modular Arithmetic I

Arithmetic mod m; viewing the integers modulo m as a number system.

Gross-Harris, Chapter 15

Monday, March 21: Modular Arithmetic II

Another way of looking at modular arithmetic; computations in modular arithmetic.

Gross-Harris, Chapter 16

Wednesday, March 23: Modular Arithmetic III

Inverses in Modular arithmetic; reinterpreting linear diophantine equations.

Gross-Harris, Chapter 17

Friday, March 25: Fermat's Little Theorem

Computing powers in modular arithmetic; statement of Fermat's little theorem.

Gross-Harris, Sections 18.1-18.5

March 26 through April 3: Spring Break (no class)

Monday, April 4: Computing Powers Modulo p

Two proofs of Fermat's little theorem; computing ridiculously large powers of numbers modulo p.

Gross-Harris, Sections 18.6-18.7

Wednesday, April 6: Computing Roots Modulo p, part I

Existence of roots modulo p; computing roots modulo p.

Gross-Harris, Chapter 19

Friday, April 8: Computing Roots Modulo p, part II

More practice computing roots modulo p.

Gross-Harris, Chapter 19

Monday, April 11: Review

Wednesday, April 13: Second Midterm Exam

Friday, April 15: Euler's Theorem

The Euler phi-function; statement and proof of Euler's theorem.

Gross-Harris, Sections 13.2-13.4 and Section 20.1

Monday, April 18: Computing Powers Modulo m

More computations in modular arithmetic; computing inverses as powers.

Gross-Harris, Sections 20.2-20.4

Wednesday, April 20: Computing Roots Modulo m I

Adapting root computation techniques to general moduli.

Gross-Harris, Section 20.4

Friday, April 22: Computing Roots Modulo m II

Roots modulo m as a generalization of roots modulo p.

Gross-Harris, Section 20.4

Monday, April 25: How to Build Codes I

Types of codes; historical examples.

Gross-Harris, Chapter 21

Wednesday, April 27: How to Build Codes II

Public-Key Cryptography; RSA codes; coding and decoding, applying powers and roots modulo m.

Gross-Harris, Chapter 22

Friday, April 29: Distribution of Primes

Factorizing numbers on a computer; the prime number theorem; prime deserts.

Gross-Harris, Sections 23.1-23.2

Monday, May 2: Primality Tests I

Pseudoprimes; primality tests; how to find large primes.

Gross-Harris, Sections 23.3-23.6

Wednesday, May 4: Primality Tests II

Strong pseudoprimes; better primality tests.

Gross-Harris, Sections 23.7-23.9

Friday, May 6: Generators Modulo p

Generators mod p; counting generators.

Gross-Harris, Chapter 24