2 (number)

2 is a natural number that lies between 1 and 3. It represents the quantity of a pair. In Hindu-Arabic numerals it is written "2", in Roman numerals "II", and in binary "10".

In mathematics and language, 2 plays a special role. It is the only number that is simultaneously prime and even. It is also the basis for distinguishing numbers into even and odd categories.

Mathematical properties

The number 2 has exactly two divisors: 1 and itself — this is the definition of a prime number. Adding 2 to itself, multiplying it by itself, and squaring it all yield 4. This property (x+x = x·x = x²) is unique to 2 among positive integers. Additionally, 2 is the base of binary arithmetic, the system on which computers operate.

Every even number is divisible by 2. When a number is divided by 2 with a remainder of zero, it is called even; if the remainder is 1, it is odd. The powers of 2 (2, 4, 8, 16, 32…) form the basis for computer memory capacity measurements.

Use in language

Many languages have a special form to refer to a pair of things (the dual number). In Somali, nouns have a dual form, for example "laba buug" (two books) rather than the general plural "buugag". Words such as "labo-geesood" (two-sided) and "labajibbaaran" (paired) derive from the same root.

Symbolism and culture

Across different cultures, 2 is associated with ideas of duality and contrast: night and day, female and male, right and left. In some philosophical systems, such as the concept of binary opposition, reality is understood as composed of two complementary parts.