that was my original solution, but then it timed out. how?

Hi!
Where can I see the theory according to these formulas?
it's not the first time I've met such problems, and some calculate the sum of a series using a simple formula.

^^

Rejected, should be rewritten due to issues pointed out below, and author has been inactive for more than 3 years.

fixed by someone

This is good.

This is a only math solution!!!

It's best.

4000 tests?????
Flipped stuff in Assert::That...
Never put the reference solution in the Preloaded, and it's in global scope anyway (put it in another scope.)

I think that the string is not trimmed in random tests:
Expected: equal to muIcKiTXBKIdGdTwFMFnAxdtEUrRClWvsMPdJxay lPduzTkLMLxay
Actual: muIcKiTXBKIdGdTwFMFnAxdtEUrRClWvsMPdJxay lPduzTkLMLxay

After adding char in front and in end
Expected: equal to PIPay
Actual: PIPay

You're right - my mistake that I didn't do it

Thank you for the translation, approved :-)