1 (number)

1 (also called mid or kow in Somali) is the number that follows 0 and precedes 2. It is the first of the natural numbers and is an integer. The standard symbol for it in Hindu-Arabic numerals is "1".

In mathematics, 1 has a particular role: it is the multiplicative identity element, meaning that any number multiplied by 1 equals itself (a × 1 = a). Also, 1 raised to any power always equals 1 (1ⁿ = 1).

Mathematical properties

1 is not counted among the prime numbers, because a prime number must have two distinct divisors. It is also not a composite number. For this reason, the fundamental theorem of arithmetic would face difficulties if 1 were classified as prime, since prime factorization would no longer be unique.

In abstract mathematics, the multiplicative identity element is denoted "1" or "e" in group theory. In matrix algebra, this role is filled by the identity matrix. Similarly, 1 serves as the basis for the definition of a unit in measurement.

Other notations

In Roman numerals it is written as I. In the binary system (base 2), 1 and 0 are the only two symbols used, and they form the foundation of computer arithmetic. In logic, 1 is commonly used to represent the value "true".

Related notations include 0.1, and −1, which is the additive inverse of 1. 0.1 is a decimal fraction that is less than 1.