Let \(\frac{1}{x_{1}},\frac{1}{x_{2}},\ldots,\frac{1}{x_{n}}\left( x_{i} \neq 0 \right.\ \) for \(\left. \ i = 1,2,\ldots,n \right)\) be in A.P. such that \(x_{1} = 4\) and \(x_{21} = 20\). If \(n\) is the least positive integer for which \(x_{n} > 50\), then \(\sum_{i = 1}^{n}\mspace{2mu}\left( \frac{1}{x_{i}} \right)\) is equal to\\