The bone (pictured below), estimated to be more than 20,000 years old, is a baboon's fibula and was discovered to have many markings engraved into it. The bone was first thought to be a simple tally stick. However, upon further investigation, many scientists and mathematicians believe that the markings are indicative of a mathematical understanding that transcends basic counting.
Some of the more striking features of the bone include a column of three notches that double to six, a column of four notches that double to eight, and ten notches that halve to five; these are all indicative of a basic understanding of doubling or multiplication.
Even more curious is the fact that all the numbers in the other columns are odd and one of those columns consists of all the prime numbers between 10 and 20. The fact that there are prime numbers clearly separated would indicate some understanding of division.
There are tally sticks that have been discovered that predate the Ishango Bone. However, the Ishango Bone is the oldest one known that contains logical carvings giving evidence of a deeper mathematical understanding.