Complexity class of an algorithm What is the complexity class of an algorithm that runs in $n^{\mathcal{O}(\sqrt{n}log(n))}$ time? 

As $n$ gets large $\sqrt{n}log(n)$ increases at a very slow rate. Does this mean that the algorithm has the same complexity as $n^{\mathcal{O}(1)}$, which would be in $P$?
No, $\sqrt{n}$ increases far faster than $O(1)$, and $n^{\sqrt{n}}$ grows far faster than $n^{O(1)}$.  No, it certainly does not have the same runtime.  See Sorting functions by asymptotic growth.

There may be no predefined complexity class; the complexity class is the class of all algorithms who run in time $n^{O(\sqrt{n} \log n)}$, and there's probably not much more to say.