from http://www.math.siu.edu/kocik/seven.htm

European restrooms are coded geometrically — a triangle for the gentlemen and a circle for the ladies. The symbols may represent two numbers: the number three for the triangle and the number four for the circle (in the symbolism of most civilizations, a circle represents number four). And with this we are entering an archetype that may be summarized into the oldest spiritual equation: 3+4=7.

The figure below shows a 16-th Century alchemic drawing by Albert Durer. The alchemic meaning of the union of a square inscribed in a triangle is juxtaposed with the figures of a male and female in the center!

Also, the “Rebis” (figure at top) does not leave any doubts as to the symbolic numerical values of these geometric forms as used in the esoteric sciences: the union of 3 and 4 is associated with the seven astrological planets (spiritual planes of existence). Notice also the Rebis (“two-thing”) — the alchemical Hermaphrodite — the perfect union of opposites. (Rebis is believed to possess knowledge beyond the mundane realms.) The formula 3 + 4 = 7 appears as the central structural element of the contents of the cosmic proto-egg — a clear promotion of its primordial significance.

Hermeneutic tradition also considered the number 7 as being split into the spiritualthree and the material four. This was the basis for the partition of the seven liberal arts, the famous trivium and quadrivium of medieval universities.

Africa. Dogons, who live in the Middle Niger River region, view seven to be of a special importance in their metaphysical system. Quite remarkably, the symbolism of this number is also based on the equation 3+4=7. Like in ancient Europe, Dogons associate the number three with the man, and the number four with the woman; therefore number seven symbolizes perfection. The accordance with the alchemical symbolism is striking. Dogons employ this symbolism in everyday customs: a woman’s dress is made of four woven strips, while man’s trousers are made from three sets of three strips.

Pythagoreans. The extension of 3 and 4 into odd and even is especially intriguing, for Pythagoreans too considered odd numbers as masculine and even numbers as feminine. [Although they lived more than 2 millennia ago, the Pythagoreans are not the first to be known for this distinction. In Sumerian — the language of the civilization that invented writing c. 3000 BC — the word for 1 (gesh) originally meantman, male, penis, and 2 (min) meant woman.]

Pythagoras did not give any special significance to the number seven nor to the equation 3+4=7. However, the numbers three and four do incidentally play a role in the famous Pythagorean theorem on right triangles. The most exemplary is the integer-sided triangle with legs of lengths 3 and 4:     3² + 4² = 5²

America. A similar basis for the importance of the number seven is found on the other side of Atlantic! Mayans believed that the sky had seven layers. Their archetypal seven was also split into 3 and 4, but the association was reversed: 3 was associated to woman and 4 to man. Their conjunction, 7, was able to produce, therefore was endowed with life! [This inverted association can also be found among the Akan people of Africa who associate 3 to the Queen Mother, and 4 to the King.]

Labyrinth. Yet another archetype that comes into mind is the pattern of a “labyrinth,” depicted the figure above. It should not be confused with the labyrinth of Minotaur, for it is impossible to get lost in it. Its circular path leads you in seven turns right into the center. Although commonly associated with ancient Greeks, this archetype is much older and, curiously enough, widely spread in the ancient world. One classical copy comes from a clay tablet of Pylos (2000 BC), but the same pattern can be found on rocks in Spain (~4000 BC), and many copies in stones have continually been rebuilt on shores of Scandinavia since unknown times. The pattern seems to be a remnant of a vanished Megalithic civilization that sprang from Northern Europe and found its end with the arrival of Indo-European folks. (Surprisingly, the pattern is believed to be known to the pre-Columbian Navahos.)