I want ask Mathematica at wolframalpha for ...
   (sorry: I had formatted it in Mathjax, so I take a screenshot for my question here)

$$ \lim_{n \to \infty} \exp(x \cdot (n+1)) \sum_{k=0}^n \left( (n+1-k)^k {(-x \exp(-x))^k \over k! }\right) $$
and put it in various notation styles, one of them     

    Limit [ exp(x*(n+1)) * sum[ (n+1-k)^k *((-x) *exp(-x))^k/k!, k=0 to n], n -> infinity]


but WA always complains it cannot understand...    

***Q:*** What am I doing wrong?        

*(If I ask partial expressions from this it* **can** *understand them)*