The number 9 is a natural number that comes after 8 and before 10. It is the largest single-digit number in the decimal system and has significant mathematical properties, including being the first odd composite number and a refactorable number. In mathematics, 9 is unique because it is the only square number that is the sum of two consecutive positive cubes (9=13+239=1^3+2^39=13+23). It also plays a role in various mathematical tests such as casting out nines. Beyond mathematics, the number 9 has cultural, religious, and scientific significance. For example, it symbolizes completeness in the Baháʼí Faith and has importance in Hinduism and Norse mythology. Scientifically, the term "nines" often relates to purity in chemistry, and human pregnancy typically lasts nine months. Additionally, "9" is the title of a 2009 animated post-apocalyptic science fiction film directed by Shane Acker, featuring a rag doll named "9" who awakens after humanity's extinction. The film explores themes of survival, intelligence, and sacrifice in a machine-dominated world. This broad overview covers the main aspects of 9 as a number, cultural symbol, and film title.
