Inka Numbers, Khipu, and Yupana: a Reanalysis

Abstract We review the history of decipherment on the technologies used for numbers by the Inkas – khipus and yupanas . We offer a novel interpretation of the portable “checkerboard” yupana drawn in 1615, revealing a numerical algorithm. This analysis sheds new light on the Inka number system, questioning its inclusion of a concept of zero and its interpretation as a positional system. We conclude that Inka numbers and computational methods were likely non-positional, analogous to Mesopotamian, Egyptian, Greek, and Roman numbers. We show the Inka multiplication method as similar to – but more efficient than – the Egyptian method in the Rhind Papyrus. This analysis shows the Inka number system to have ranked among the great mathematical traditions of the ancient world.