Alex Bellos describes a fascinating interplay between culture, mathematics, and stamps in his Nov. 4, 2014 posting on the Guardian-hosted Alex’s Adventures in Numberland,
According to Chinese legend a turtle like the one above crept out of the Yellow River about 4000 years ago. It looks like it is riddled with spots, or bullet holes. But if you look carefully, the dots on its back represent the digits from 1 to 9 arranged in the following way:
If you add the numbers in each row together, they are all equal to 15. For example 4 + 9 + 2 = 15, and so on.
If you add the columns, they sum to 15 also. For example, 4 + 3 + 8 = 15. And yes, you guessed it, the diagonals do too.
A grid containing consecutive numbers starting from 1 such that rows, columns and diagonals all add up to the same number is known as a magic square. The 3×3 square on turtle is known in China as the lo shu.
Magic squares have long fascinated soothsayers, herpetologists, mystics, architects, soldiers, artists, mathematicians…and now, stamp collectors. Macau, the former Portuguese colony now a part of China, has just issued a set of magic square stamps that, it claims, not only promotes Chinese culture but also creates a “unique product in the history of philately.”
I encourage you to read the post in its entirety as Bellos follows the magic square through a number of time periods and cultures.