You can download A Classical Introduction to Modern Number Theory 2nd edition by Kenneth Ireland and Michael Rosen free in pdf format.
About Book
This well-developed, accessible text details the historical development of the subject throughout. It also provides wide-ranging coverage of significant results with comparatively elementary proofs, some of them new. This second edition contains two new chapters that provide a complete proof of the Mordel-Weil theorem for elliptic curves over the rational numbers and an overview of recent progress on the arithmetic of elliptic curves.