Short Sharp Science: Deceptive puzzle may be solved after 74 years: "The Collatz conjecture was proposed by Lothar Collatz in 1937. It is also known as the '3n 1 problem' because of its deceptively-simple definition.
Now mathematician Gerhard Opfer of the University of Hamburg, who was a student of Collatz, says he has proved the conjecture true.
The problem starts by choosing any whole number, n. If n is even, divide it by 2. If n is odd, multiply it by 3 and add 1 to get 3n + 1. Collatz believed that if you keep repeating these operations on the resulting numbers, no matter what your starting number, the result will always reach the number 1 eventually.
This has been verified for numbers up to 5.76 x 1018 (nearly 6 billion billion), but without a proper mathematical proof there is always the possibility that an incredibly large number could violate Collatz's rule."
Update: the proof doesn´t seem watertight
