There is a repeated element 84
in the list, thus array.index
does not work as you expected it to be. Also, your code has a quadratic complexity which is not required.
To fix your code with a minimum amount of edit, it would look something like this:
array = [-37,-36,-19,-99,29,20,3,-7,-64,84,36,62,26,-76,55,-24,84,49,-65,41]
print sum(array[i] for i in range(len(array)) if i % 2 == 0)*array[-1] if array != [] else 0