I have this sum, which probably doesn't exist in closed form.
$\displaystyle S(\mu,\lambda,n,M,l)=\sum_{\alpha=1}^{\mu}\frac{1}{\alpha!}\Big(1-\frac{\alpha(2\mu-\alpha)(M-2l)}{2n\mu^2}\Big)^{\lambda} \leq \sum_{\alpha=1}^{\mu}\alpha^{\alpha+\frac{1}{2}} e^{-\alpha+\frac{\alpha \lambda(2\mu-\alpha)(M-2l)}{4n \mu^2}}$ using Stirling number approximation and upper bound on $(1-\frac{k}{n})^n$.
Any ideas on how to find an asymptotic approximation for it would be massively appreciated. Please don't solve it for me, just give some hints/advice. Thanks
$\mu, \lambda,n,M$ are constants and $l$ is a variable. It will be used in the next summation of the form $S(\mu,\lambda,n,M,c)=\sum_{l=0}^{\frac{M}{2}-1}\frac{1}{c-S(\mu,\lambda,n,M,l)}$