It's not testing all values, but one particular starting point. In all likelyhood, it will never reach its stopping condition from this starting point, but prov

It's not testing all values, but one particular starting point. In all likelyhood, it will never reach its stopping condition from this starting point, but proving this even for a single value is currently intractable. Compare with the "5x + 1" variant of the Collatz cojecture, where many values are believed (but not proven) to run off to infinity, never to return.