Problem in expression
maybe you meen
i <= 2 * n
This expression is error.
Please do not use such large screenshots for illustrating an error. It is hard to read, especially in browser on a smaller window size.
From what I can see, in your code you have a compiler error on the expression “2n”.
That is not legal syntax. I guess you want to express “2 times n”, which you write down as “2 * n” in most programming languages.