Papers by Peter Schorer describing several new approaches.
Observations posted by Ken Conrow to stimulate further research.
From Eric Weissten's World of Mathematics. Article with references and links.
Katholische Universität Eichstätt, Germany; 5--6 August 1999. On-line proceedings and group photo.
Results up to 2^60 by Tomás Oliveira e Silva.
A paper by Craig Alan Feinstein arguing that the Collatz Conjecture cannot be formally proved.
By Andrew Shapira. The intensity of a point denotes the time taken to terminate.
Properties and predictive models for the Collatz Problem and related functions.