In this book, which shows besides definitions a choice of basic theorems, corollaries, conjectures, and formulae which are important in number theory, you will find no proofs. For better understanding, in some cases, also special theorems are given in addition to the most general ones. In reading a chapter, you should be able to get in a few hours first information, find a base for further developments, or repeat known facts.The choice of theorems and formulae is arbitrary and strictly focused on number theory. The main source is the author's sequence of studies in number theory. You will find more information in the selected literature at the end of the book.