This book has been growing over the years out of several resources. Firstly, the courses in number theory and modern algebra I had occasionally been teaching at UNC Charlotte. Secondly, my interest to invent mathematical problems for competitions, and invent and pose problems for individual work with gifted students. After being forced to retire about two years ago because of health reasons, I did continue to occupy myself with these topics, and I learned more substantially from the work of Gauss on quadratic reciprocity and on the construction of Fermat polygons. Too, I did take up numerical computation with the computer language of Dr. Racket, which is based on Lisp and freely available on the internet.