That is: prove that

Did your try this with n= 1, 2, 3, etc. first? If n= 1, n-1= 0 and is not defined. if n= 2, so that sum is . If n= 3, so the sum is .

In order for that sum to make sense, n-1 must be a power of 2 so n must be one more than a power of 2. For example, if n= 5, n-1= 4 and so the sum is .

You can't prove this- it is not true. Whatcanbe proven is that if n is a power of 2 (1, 2, 4, 8, etc.) then or, more simply, .