The origin of the ninth power equal to 15 comes from that ancient book.

According to legend, Jiugongge was created by Ou Yangxun, a calligrapher in the Tang Dynasty. Ou Yangxun's Inscription of Liquan in Jiucheng Palace is a masterpiece in his later years, which is rigorous, vigorous and complete. It has always been praised as the "first official book" by scholars, with many imitators.

Jiugongge is the "predecessor" of Sudoku, which originated in China. Thousands of years ago, our ancestors invented Luo Shu, which is more complicated than Sudoku now. It requires that the sum of the numbers in the vertical and horizontal directions is equal to 15, rather than a simple number of nine that cannot be repeated. Nine palace map in the Confucian classic "Book of Changes" also originated from this, so it is called "Luo Shu Nine palace map". Because of its important position in the history of China's cultural development, the name of "Nine Palaces" has been preserved to this day.