  In the middle of the third millennium BC the Sumerians must have noticed that
the reciprocal of the number 7,in contrast to the numbers 1,2,3,4,5,and 6,could
not be expressed by a finite sexagesimal fraction but it recurred every three
places.Since the number 7 is the first natural number that has such a property,
it was of particular interest to them and became the representative of their
number mysticism.
