Two minor suggestions since this is probably targeted to people new to coding/codewars:

1- adding a breakdown of one of the sums, like:
sum(5) = 1 + 2 + 3 + 4 + 5 = 15

2- adding to the end of the description the largest number tested, and a disclaimer that if the solution is timing out, the code needs to be reviewed or a non-brute-force solution has to be thought out

I'd say this problem is 8 kyu, if you want this to be 7 kyu maybe add an extra dimension where instead of a long the user has to work with a string array and concatenate those values.

Why it doesnot take float or exponential value!?
You should have mentioned that in your kata description.

When I do the test cases my code works but when I click "ATTEMPT" I have no result because my code takes a long time to execute, I have tried both with "while" and with "for" and the same thing happens to me, it is my fault or there is some error?

I agree with others that this is too simple and duplicates a number of other katas. It would be more interesting if the range spanned positive and negative integers, i.e. (m,n) ∈ ℤ, not just (1,n) ∈ ℕ, and do both m < n and m > n. It could still be tackled as both O(1) and O(n), as the coder wishes.

In my opinion waaaay to easy, I think we already have tons of similar katas here. It could be made better tho:

• allow numbers beyond long, disallow library BigInteger class
• introduce timing constraints, reject loop based soltions (if possible)

What kind of number n can be? Is it always greater or equal to 1 or it can be less than 1,too? Should we implement all cases or only where n>=1? I think, it would be great to add this to the Description.

This has already been raised as an issue, but in Python some methods time out. The test cases should be made smaller.

Duplicate to many katas.

This requires math knowledge but that's it.
The current tags are "fundamentals, basic, practice, loops"
Not sure that "loops" and "fundamentals" are relevant

The compiler showed an error if the required function was built within the class as an inline function although worked fine when defined outside the class

not sure if i can soup up my code anymore I am pasing 20 with 0 wrong at 420ms but still running into memorry error after using a couple mem optimizing tricks

Because your tests are mostly around big numbers I would suggest adding one line to description suggesting users to find a formula instead of using loops. I guess it'll be useful for newcomers :)