I am assuming that "" is scalar and hence taking it as "r", but that shouldn't matter for this question. Also please initialize r, k before attemting to run the code. Here is the sample code:
sum = 0;
for n = 0:k-1
if mod(k+n, 2) == 1
sum = sum + (2*n+1)*r;
end
end
Note: This is not an optimized code and you may write a more optimized implementation.