The number 4 is a natural number that follows 3 and precedes 5. It is a square number (since 2×2=42\times 2=42×2=4), the smallest semiprime, and a composite number
. In mathematics:
- The square root of 4 is ±2, meaning both +2 and -2 are roots because 2×2=42\times 2=42×2=4 and (−2)×(−2)=4(-2)\times (-2)=4(−2)×(−2)=4
- The fourth power of a number nnn is n4=n×n×n×nn^4=n\times n\times n\times nn4=n×n×n×n
- Four is involved in many fundamental concepts such as the four elementary arithmetic operations (addition, subtraction, multiplication, division)
- A four-sided plane figure is called a quadrilateral or tetragon
- The four-color theorem states that any planar map can be colored with four colors so that no adjacent regions share the same color
Culturally and symbolically, 4 is significant in many traditions: it represents the four elements (earth, air, fire, water), four seasons, and four cardinal directions
. However, in some East Asian cultures, it is considered unlucky due to its phonetic similarity to the word for "death"
. In summary, 4 is a fundamental number with mathematical, cultural, and symbolic importance, representing completeness and structure in various contexts
