Yi Xing
Shen wrote extensively about what he had learned while working for the state treasury, including mathematical problems posed by computing land tax, estimating requirements, currency issues, metrology, and so forth. Shen once computed the amount of terrain space required for battle formations in military strategy, and also computed the longest possible military campaign given the limits of human carriers who would bring their own food and food for other soldiers. Shen wrote about the earlier Yi Xing (672–717), a Buddhist monk who applied an early escapement mechanism to a water-powered celestial globe. By using mathematical permutations, Shen described Yi Xing's calculation of possible positions on a "go" board game. Shen calculated the total number for this using up to five rows and twenty five game pieces, which yielded the number 847,288,609,443.