We intended to write this book simple and easy enough for those
mathematics majors in their sophomore year or above while boiling down
some of the contents to make it appropriate as a semester long number
theory textbook without including quadratic congruences, sums of
squares, and continued fractions. This book is not only suitable for
those graduate students in mathematics as a number theory seminar
reference who are not majoring in number theory, but also for those
gifted juniors and seniors in high school as a guidance who are
preparing for the International Mathematics Olympiad.