the code turned out very interesting

yeah I totally agree

Approved with a new reference solution.

that's pretty fast by the standards of the universe

Translate Dart

check my solution

It depends, if the kata is bumped up by a recent description edit or language update, translating it would reduce the time of waiting as it is more likely that someone will chime in and review it, but consider yourself lucky if it's within few months or so ^^

how long does it take to check a translation of a kata?

Dart translate

Looping for big inputs takes lots of iterations, which can take a long time.

Many katas are this way, they only require pretty much some further mathematical research.

This kata is "Google the formula" instead of "Show your programming skill"...

Thanks, I'll try.

Keeps failing the "ATTEMPT". "TEST" doesn't fails because is using only 3 numbers to test it. I think it can be due large numbers or too much calculations. Mine rises to 50 passed then times out.

Your code being too slow is not a kata issue. Your idea for s is good, but you need something better than sum to calculate z.