The number 9 is the natural number that comes after 8 and before 10, and it has several interesting mathematical and cultural facets. Here’s a concise overview:

• Mathematics
  • 9 is the fourth composite number and the first odd composite number.
  • It is a square number: 3^2 = 9.
  • It is the sum of the cubes of the first two positive integers: 1^3 + 2^3 = 9.
  • Casting out nines is a traditional quick-check technique for arithmetic in decimal.
  • 9 is the largest single-digit number in the decimal system.
• Cultural and media references
  • In film, “9” refers to a 2009 animated science fiction movie about a post-apocalyptic world featuring a rag doll named 9.
  • The number appears in various lists, puzzles, and numerology discussions.

If you’d like, specify the angle you’re most interested in (pure math properties, number theory curiosities, historical uses, or a particular media reference), and a more detailed, focused explanation can be provided.