Did you know that the number 7 is the only number what does not fit in a circle? i mean, when you try to construct a heptagon (7-sided) in a circle, you cannot make it precisely. The angle to use is not a regular number like when you divide a circle into 2,3,4,5,6,8,9 or 10 pieces, but it is an infinite number (51,428571428571428571428571428571.. degrees. Note the returning sequence in this number).

this is one reason the number 7 is a holy number for many. It cannot be drawn with just the euclidian tools (straight ruler and pair of compasses).

Another reason that 7 is considered holy is that it comes after 6. which seems logical, but if you count 6-based, then 7 is the next round, the new beginning. As you can learn on my page about 6 there is a lot to say to count 6-based. The ancients did it long time ago, thats why we have 12 hours in a clock.