The Structure of the 3x + 1 Function - Papers by Peter Schorer describing several new approaches. Collatz 3n+1 Problem Structure - Observations posted by Ken Conrow to stimulate further research. Collatz Problem - From Eric Weissten's World of Mathematics. Article with references and links. The 3x+1 Problem Conference Proceedings - Katholische Universität Eichstätt, Germany; 5--6 August 1999. On-line proceedings and group photo. Computational Verification of the 3x+1 Conjecture - Results up to 2^60 by Tomás Oliveira e Silva. The 3x+1 Problem Annotated Bibliography - By Jeffrey Lagarias, 1997. The Collatz 3n+1 Conjecture is Unprovable - A paper by Craig Alan Feinstein arguing that the Collatz Conjecture cannot be formally proved. An Image from the Collatz Problem - By Andrew Shapira. The intensity of a point denotes the time taken to terminate. The Generalised 3x+1 Problem - A survey by Keith Matthews. The Collatz Problem, data and models - Properties and predictive models for the Collatz Problem and related functions.