Jeffrey C. Lagarias writes this document on the 3x+1 problem also known as Collatz problem and the Syracuse problem. Read an introduction and generalizations.

International conference discussed the Collatz Problem and related topics. Download papers and abstracts of talks given during the proceedings.

Author Eric W. Weisstein presents a long and detailed explanation of Collatz Problem with hyperlinks and includes a list of linked references.

Provides papers and notes by Peter Schorer on the 3x+1 problem, Fermat's Last Theorem, and Goldbach's Conjecture. With book info on various math-related subjects.