The Ishango bone is a bone tool handle discovered around 1960 in the African area of Ishango, near Lake Edward. It has been dated to about 9,000 BC and was at first thought to have been a tally stick.
At one end of the bone is a piece of quartz for writing, and the bone has a series of notches carved in groups on three rows running the length of the bone. The markings on two of these rows each add to 60. The first row is consistent with a number system based on 10, since the notches are grouped as 20 + 1, 20 - 1, 10 + 1, and 10 - 1, while the second row contains the prime numbers between 10 and 20! A third seems to show a method for multiplying by 2 that was used in later times by the Egyptians. Additional markings suggest that the bone was also used a lunar phase counter.
The Ishango bone is kept at the Royal Institute for Natural Sciences of Belgium in Brussels.
1. Bogoshi, J., Naidoo, K., and Webb, J. "The Oldest Mathematical Artifact." Math. Gazette, 71: 458 (1987).
2. Heinzelin, J., de "Ishango." Scientific American, 206 (6): 105-116 (Jun. 1962).