I used this and it worked.

long result=hammings[n-1];
return result;

I don't know why, but I'm just happy it passed. Oh well :/

It's also inconsistent. This time I changed nothing but the debug outputs, and the first sample test passed. Here is the debug code and the output.

Console.WriteLine("List count="+hammings.Count);
Console.WriteLine("n-1="+(n-1));
Console.WriteLine("Going to return: hammings["+(n-1)+"]="+hammings[n-1]);
return hammings[n-1];

List count=7
n-1=1
Going to return: hammings[1]=2
System.ArgumentOutOfRangeException : Index must be within the bounds of the List.
Parameter name: index

I mean, hammings[n-1] is fine and contains the correct value when used inside Console.WriteLine, but it raises an exception when I'm trying to return it. I believe this is a problem with the website. I have checked for n=0 beforehand. For the first sample test, the hammings list contains four elements, and n-1==0. It still raises the exception.

The last two lines of my code are

Console.WriteLine(hammings[n-1]);
return hammings[n-1];

The console gave the correct answer, but when I returned the value it raises the following error:

System.ArgumentOutOfRangeException : Index must be within the bounds of the List.
Parameter name: index

I am 100% certain the value of n can't change between the two lines... anyone know why this bug exists?