Two views if the Ishango bone (Lake Edward, Zaire, 300 000 B.C.) indicating that a calendrical or numeration system was known to the fishing and hunting folk of the area. Its schhematic drawing shows the arrangement of notches visible to the naked eye, that suggest a knowledge of multiplication by two and of prime numbers (C.Zaslavsky: Africa Counts, Lawrence Hill Books, New York, 1990, page 21).