lochas esi

This is really cool, if you want to waste your coworkers time

Yoo, so unreadable. And one more thing. You don't have a check for the input parameter to be less than zero.

This solution is 8 times slower. "For" and "if" are better.

ты лох

Why Kata test excludes negative number?

Along with already mentioned problems, negative number will break this.

Run your method with Linq implementation ten times for n=50_000_000 and you will see why :) Linq-based solutions usually call for O(n) solutions. The kata can be solved in O(1). Why run a loop n times when you can solve the problem witohut a loop?

why shouldn't it?

...except it should not be used in this kata.

Linq is my god

I somewhat agree although there's a solution below that just uses new lines a little more effectively with the same methods that I think is easier to read.

Great solution

The second parameter of Range is count, so the range is from 0 to n - 1