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.
Related entry Lebombo bone
Related category HISTORY OF MATHEMATICS
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