Evolutionary psychologists: 7 is a recurring pattern because of the days in the week. Archetypes: 7, masks, trickster, fool, mother, father. Carl jung: elements within us that want to shine through. Greek anthology: probably written by metrodorus, a collection of riddles and mathematical puzzles. Charlemagne: established the holy roman empire, hired alcuin to write puzzles and educate masses. Decimal number system: led to/allowed for banking(helped bring europe out of the dark ages. The rabbit puzzle: fn = fn-1 + fn-2.