An Introduction to the Theory of Numbers (Hardy)

I had the great good fortune to have a high school mathematics teacher who had studied number theory. At his suggestion I acquired a copy of the fourth edition of Hardy and Wright's marvellous book An Introduction to the Theory of Numbers. This, together with Davenport's The Higher Arithmetic, became my favourite introductory books in the subject. Scouring the pages of the text for clues about the Fermat problem (I was already obsessed) I learned for the first time about the real breadth of number theory. Only four of the chapters in the middle of the book were about quadratic fields and Diophantine equations, and much of the rest of the material was new to me; Diophantine geometry, round numbers, Dirichlet's theorem, continued fractions, quaternions, reciprocity ... The list went on and on.