#2015_23 Riemann is hiding?

Calculus Level 3

\[f\left( n \right) =\frac { 1 }{ n } { \big\{ (2n+1)(2n+2)\ldots(2n+n) \big\} }^{ 1/n },\]

then what is \(\displaystyle \lim _{ n\rightarrow \infty }{ f\left( n \right) }? \)