Let $ x_{1}\geq x_2\geq\cdots\geq x_{n}\geq0$, and $\sum\limits_{k=1}^{n}x_{k}=1$. What is the maximal value of$$\sum_{k=1}^{n}x_{k}^{2}\sum_{k=1}^{n}kx_{k} ?$$
I think, Maybe we could try Rearrangement inequality
or
let $x_n=a_n,x_{n-1}=a_n+a_{n-1} , \dotsc, x_1=a_1+a_2+\dotsc+a_n$
where $a_i\geq0$
I am really grateful for any help
EDIT: I am very sorry, $1$ is not the upper bound for all $n$, but I guess $\sum\limits_{k=1}^{n}x_{k}^{2}\sum\limits_{k=1}^{n}kx_{k}\lt2 .$
For $n=5$$$x_1=0.926599, x_2=x_3=x_4=x_5=0.0183503$$LHS $=1.01773\gt 1$