Origin:
China's 99 multiplication table originated very early. At the latest in the Spring and Autumn Period in Lu Huangong, it was written in Guanzi during the Spring and Autumn Period and the Warring States Period. It is mentioned in the book that "An Opera should be the number of 99 to meet the heaven". In the Warring States period, the formula of 99 was quite popular, and various philosophers' works, such as Xunzi, have cited the phrases of multiplication formula as scientific arguments. The multiplication formula (multiplication table) in ancient China was from "9981" to "224", and its order was opposite to that of later generations.
Baidu entry excerpt:
The multiplication formula is the basic calculation rule for multiplication, division, square root and other operations in ancient China, which has been used for more than two thousand years. In ancient times, the multiplication formula was from top to bottom, from "9981" to "one is the same as one", which is contrary to the order used now. Therefore, the ancients used the word "999" at the beginning of the multiplication formula as the name of this formula, also known as "999 Table", "999 Song" and "999 Multiplication Table".
99 multiplication table picture: