That also is incorrect - the sequence either converges to one or a stable cycle - not infinitely. That's also a horrible question for illustrating functional p

That also is incorrect - the sequence either converges to one or a stable cycle - not infinitely. That's also a horrible question for illustrating functional programming style. It would be much more efficient to have a simple loop caching the array n->f(n) and then finding the ones that converge to 1.