Find a permutation $\sigma$ maximizing the sum $\sum_{i=1}^n {a_i \over \sigma(i)}$.

48 Views Asked by At

Given $$a_1< a_2<\dots < a_n,$$

find a permutation $\sigma$ maximizing the sum >$$\sum_{i=1}^n {a_i \over \sigma(i)}.$$

I can't figure our where to begin. I know that the solution is $\sigma=e$, but I cannot prove it.