Early Thought Patterns: A Prehistoric Esthetic of Number
In addition to practical arithmetic functions for numbers, ancient peoples also developed esthetic concepts pertaining particularly to the numbers two, three, four, and seven. These concepts were also philosophical, and terms from them are part of our vocabulary (The "dead center," "going off the deep end," etc.) Though we no longer know where they came from. The ideas seem to have been universal: I personally witnessed evidence for this in Africa, Australia, America, and Norway.