Źródło TeX:

x^x_N =\frac{1}{N}\sum_{n=0}^{N-1}{x_n=}\frac{1}{N}\left[\sum_{n=0}^{N-2}{x_n+x_N}\right]=\frac{1}{N}\left[(N-1){\overline{x}}_{N-1}+x_N\right]