The Ishango bone, found in the Congo and potentially 20,000 years old, contains a series of tally marks that may demonstrate some of the earliest concepts of prime numbers or a lunar calendar. While prime numbers were likely not fully understood until around 500 BC, the Ishango bone and later Egyptian arithmetic incorporated some elements like multiplication by 2. Megalithic structures from 3000 BC in the UK also incorporated geometric concepts. The formal study of mathematics began in the 6th century BC with the Pythagoreans in Greece, though Chinese and Hindu-Arabic systems also made early contributions that developed over centuries and influenced Western mathematics through Islamic scholars.