Summation Question

1. The problem statement, all variables and given/known data



I need a summation where the answer is 1 2 2 2 2 2 2 2



2. Relevant equations



a(0) + sum(2*a(1) + 2*a(2) +2*a(3))



3. The attempt at a solution



I unfortunately have no idea where to start, basically it is taking a symmetrical function from 0 to N-1. where the function is symmetric from the center point.



I have an answer for it which is



a(N-1/2) + sum_n=1^(N-1)/2 (2*a[((N-1)/2) - n])



However I wanted to put it all inside the summation