Traditionally, number theory is the branch of mathematics concerned with the properties of integers and many of its open problems are easily understood even by non-mathematicians. More generally, the field has come to be concerned with a wider class of problems that arise naturally from the study of integers. Number theory may be subdivided into several fields according to the methods used and the questions investigated. See for example the list of number theory topics.

Wikibooks has a book on the topic of: Number Theory

Wikimedia Commons has media related to Number theory.

This category corresponds roughly to MSC 11-XX Number theory; see 11-XX at MathSciNet and 11-XX at zbMATH.