This text evolved over the course of teaching MAT 338 Number Theory at Gordon College, and immense thanks are due to the students through five offerings of this course for bearing with using a text-in-progress. The Sage Math team and especially the Sage cell server have made an interactive book of this nature possible online, and the Mathbook XML and MathJax projects have contributed immensely to its final form, as should be clear.

In addition, no acknowledgement would be complete without recognizing the patience of my family with respect to the days and weeks of travel, from an hour away in New England to as far away as Cape Town and India, in order to learn more about Sage and teach using Sage in the classroom. It was always with the goal in view of enriching others' lives and not just my own, and I hope I have lived up to that promise.