In this paper Gerhard Opfer claims to have solved Collatz conjecture. Looks like a strange paper to me, but I haven't studied it. How legit does it look to people more specialized in these matters? It would be cool to see it solved....
closed as off topic by Steve Huntsman, Qiaochu Yuan, Cam McLeman, Torsten Ekedahl, George Lowther Jun 2 2011 at 19:23