$$IC = \frac{\sum_{i=1}^{26} f_i(f_i-1)}{N(N-1)}$$
The IC is calculated using the following formula: index of up 2009
In conclusion, the Index of Up 2009 is a useful tool for analyzing the frequency distribution of letters in a text and detecting encryption. Its practical applications include cryptanalysis, language identification, and text analysis. and text analysis.