In statistics, the relationship between the mean, median, and mode is given by:
\[ \text{Mode} = 3 \times \text{Median} - 2 \times \text{Mean} \]
Substitute the given values:
\[ \text{Mode} = 3 \times 23 - 2 \times 21 = 69 - 42 = 27 \]
Thus, the mode of the data is 27.