Preface to the Second Edition.- Preface for Readers.- Preface for Instructors.- 1. Introduction to the Natural Numbers.- 2. Mathematical Induction.- 3. Modular Arithmetic.- 4. The Fundamental Theorem of Arithmetic.- 5. Fermat's Theorem and Wilson's Theorem.- 6. Sending and Receiving Coded Messages.- 7. The Euclidean Algorithm and Applications.- 8. Rational Numbers and Irrational Numbers.- 9. The Complex Numbers.- 10. Sizes of Infinite Sets.- 11. Fundamentals of Euclidean Plane Geometry.- 12. Constructability.- 13. An Introduction to Infinite Series.- 14. Some Higher Dimensional Spaces.- Index.