"From the reviews of the second edition: ""This book gives a profound and detailed insight at an undergraduate level in abstract and computational number theory as well as in applications in computing and cryptography. … The author has done a lot of work in providing a plenty of examples, in adding many historical comments including sketchy biographies … and in presenting the whole topic in a very accessible style. So the book can be recommended warmly for the laymen as well as for the mathematician without experience in applied number theory."" (G. Kowol, Monatshefte für Mathematik, Vol. 140 (4), 2003)"