2 (number)

2 (two) is a natural number that follows 1 and precedes 3. It is the smallest prime number, meaning it can be divided only by 1 and itself. It is also the only even prime number; all other prime numbers are odd.

The symbol '2' as written in Hindu-Arabic numerals derives from earlier Hindu notation and spread worldwide through Arab mathematicians. In other systems, such as Roman numerals, it is written as 'II'.

Mathematical properties

Every even number is divisible by 2. Two squared equals 4, and two cubed equals 8. The square root of 2 (√2) is an irrational number, a fact known since ancient Greece, and is significant for calculating the diagonal length of a square with sides of length one.

Binary system

The base-2 counting system, or binary, uses only two symbols: 0 and 1. This system is fundamental to computers and electronic devices, since two electrical states (on/off) can be represented straightforwardly. Powers of two in base 2—2, 4, 8, 16, 32—appear consistently in computer memory measurements.

Linguistic and cultural usage

Many languages have a special form for the number two, called the dual, which is distinct from singular and plural. In Somali, 'laba' serves as a numerical marker; the ordinal form is 'labaad'. In mathematics, two represents pairing, comparison, and division into two parts.