Nine

Nine is a natural number following eight and preceding ten. It is the highest single-digit number in the decimal system, which is the most commonly used number system worldwide.

Etymology

The word "nine" comes from the Old English "nigon," which itself is from the Proto-Germanic "newun." These are all cognates of the Latin word "novem," the Greek word "ennea," and the Sanskrit word "nava," all meaning "nine."

Mathematics

In mathematics, nine is a composite number, its proper divisors being one and three. It is 3 squared, and is therefore the third square number. Nine is also a Motzkin number, which relates to a certain type of path in a plane. It is the only positive perfect power that is one more than another positive perfect power, by Mihăilescu's Theorem.

Symbolism

In many cultures, nine has special symbolism. For example, in Chinese culture, nine (九) was historically associated with the Emperor of China, and the number was frequently used in matters relating to the emperor.

In other fields

Nine also has significance in various other fields. For example, there are nine planets in our solar system, nine is the atomic number of fluorine, and a cat is said to have nine lives in popular folklore.

See also

• Square number
• Composite number
• Motzkin number
• Mihăilescu's Theorem

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