I don't really know what's wrong in your code, but apparently, codewars accepts it if you use directly n , instead of declaring a new variable number = n .

But I have no idea why this happens...

Done! :D

Could you tell me in which language this error occours, please?

Approved :)

I think it is fixed now. :) Thanks for reporting.
There should be no empty vectors.

I also agree. It use to be hard for me to do a 5 kyu, or even 6 kyu, and this seemed very easy to me.

You need to create a function solution(number) wich returns the sum of every 0 < n < number such that n is multiple of 3 or 5.
For example, solution(10)
Multiples of 3 that are < 10: 3, 6, 9
Multiples of 5 that are < 10: 5
Result: 3+6+9+5 = 23

So solution(10) returns 23.

You need to create a function solution(number) wich returns the sum of every 0 < n < number such that n is multiple of 3 or 5.
For example, solution(10)
Multiples of 3 that are < 10: 3, 6, 9
Multiples of 5 that are < 10: 5
Result: 3+6+9+5 = 23

So solution(10) returns 23.

In the discription it is said that you don't need to worry about empty arrays or vectors.

Done :)

Thank you! After some time I finally got it! :)