In central equatorial Africa, someone carved four sets of notches arranged in three rows on a bone. One row contains 11, 13, 17, and 19 notches, representing all the prime numbers between 10 and 20. The other rows also appear to be mathematical in nature. It’s unclear whether they were intentional, but it’s possible this is the first evidence of human interest in number theory. The Ishango Bone was discovered in 1950.
