It's common in JavaScript to check for argument === undefined to see if an argument exists,
so I thought there is no difference between sending undefined and not sending anything,
except if you use the the arguments object which is not commonly used

I fixed it, thanks

I have updated the Sample Tests for Javascript, I hope it's more clear now

You are right, I spent most of the time on the concept, and forgot about the description and the sample tests.
But now I hate messing with the kata after it's been approved.

approved, thanks for translating

once you find the formula, you should be able to find the nth term in a constant time

I updated the description.

removed

I have updated the kata, thanks.

Approved, Thanks for translating!

Hi dolamroth, I have a question, I don't know python but I noticed that there is a referance solution inside the test case, where you don't need one to validate users solution, you already know the equation.

yes, the test doesn't show the expected and the actual value when it's BigInt, that code fixed it.

thanks for the feedback, I have removed the negative input

thanks for the feedback, I have fixed it by using BigInt, users also need to return BigInt now,
I don't know why tests worked with me before.