The number 4 is a natural number following 3 and preceding 5. It is known as a square number since 4=224=2^24=22, and it is the smallest composite number and semiprime. Mathematically, it holds several interesting properties such as being the only square number N=n×nN=n\times nN=n×n where N−1N-1N−1 is prime. Four is significant in various mathematical theorems including the four-color theorem for maps and Lagrange's four-square theorem. In culture and symbolism, 4 represents stability and universality, often linked to the cross and square shape. It appears in various disciplines as a symbol of wholeness and order. Additionally, the number 4 is considered unlucky in some East Asian cultures due to its phonetic similarity to the word for "death." In technology and everyday life, four elementary arithmetic operations are addition, subtraction, multiplication, and division. The number is also commonly used for dividing things into quarters like the directions on a compass or segments in a pizza. Some key highlights:
- Mathematics: Square number, composite, semiprime, four-color theorem, Lagrange's four-square theorem
- Culture: Stability, completeness, symbolized by the cross, unlucky in East Asia
- Practical use: 4 basic arithmetic operations, division into quarters
This snapshot provides a broad overview of the number 4's mathematical, cultural, and practical significance.
