The number seven represents a quantity of seven things: seven days, seven colors, seven continents. It comes after six and before eight, and it's a prime number, which means it can only be divided evenly by itself and one.

Seven appears everywhere in human culture and nature. A week has seven days, probably because ancient astronomers could see seven celestial objects moving across the sky: the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn. Rainbow light is sometimes described as splitting into seven distinct colors. The ancient world had seven wonders. Many stories and songs celebrate the number: “Snow White and the Seven Dwarfs,” “The Magnificent Seven,” or the seventh-inning stretch in baseball.

In mathematics, seven has interesting properties. It's an odd number and a prime number. When you multiply seven by different numbers and look for patterns, you can find sequences that feel surprising.

People often consider seven lucky, perhaps because it appears so frequently in nature and tradition. Whether or not it's actually lucky, seven certainly holds a special place in how humans think about numbers and organize their world.