In this paper, we examine what mathematics was like in seventeenth-century Joseon through the eyes of a Confucian government official. Choi Seog-jeong was a typical official, busy working in the government and researching the Confucius classics, but he was different from regular mathematicians in that he tried to mingle Confucian philosophy into mathematics. Having come into contact with Western mathematics, he also posed the very basic question as to whether there are similarities between East and West. His attempt did not succeed from our perspective, but he was successful in finding new combinatorial examples which he did not dream would be important from other viewpoints than his own.