# WolframAlpha can't calculate this limit.

Calculus Level 5

The value of this limit : $\lim_{n\to + \infty}e^{-n} \sum_{k=0}^n \frac{n^k}{k!} .$ Can be written as $$\frac{a}{b}$$, where $$a,b$$ are coprime integers.

Find $$a+b$$.

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