This image comes from the paper https://arxiv.org/pdf/1812.02202.pdf:
It's an old Korean orthogonal Latin square attributed to Choi Seok-Jeong, in the book Koo-Soo-Ryak. It's of historical interest, since it predates Euler, and he's usually the one attributed to inventing Latin squares. It's probably in the ballpark of 300 years old.
The orthogonal Latin square is simple enough (they're basically today's numbers), and I can partially read some of the characters, e.g., it begins 九九母？？宫, but I'm really struggling to recognize most of the other characters. I asked some Chinese colleagues and they can recognize more of the characters, but also struggle.