I respectfully disagree that it's another 'find the formula problem'. The author explicitly noted that we try to solve it without using a loop. Obviously, we can solve it with a loop but we need to try to come up with another algorithm. This is about optimization and, believe me, it matters. A couple of days back I had an interview for a developers role where they asked me questions about algorithms and optimization.

Cool kata.

Thanks!

Very interesting kata (although I know some people, especially newbies, may feel a bit frustrated). Just read the description carefully, take your time, do your research and everything's gonna be fine.

Fun kata and I enjoyed it (though I somewhat sympatize with the warriors who are frustrated with it). A hint: do a quick research.

ranks cannot be changed

Examine the examples, that's all I'm gonna give away.

Well, you know what the input is so you have to adjust your code.

I personally don't think this is a 6 kyu kata. Just an opinion.

Nice kata but I don't think it's 6 kyu.

Yes, I also came across this issue. Up vote!

No, you are not stupid. Just use the provided examples/tests and reread the rules & explanation. At first glance it does seem a bit unclear.