The Collatz conjecture states that the orbit of every number under f eventually reaches 1. And while no one has proved the conjecture, it has been verified for every number less than 268. So if you're looking for a counterexample, you can start around 300 quintillion.
So what is the hectare of it? If it divide to something so what is it?
Answers & Comments
Answer:
The Collatz conjecture is the simplest open problem in mathematics. You can explain it to all your non-mathematical friends, and even to small children who have just learned to divide by 2. It doesn't require understanding divisibility, just evenness.