one

One is the integer that follows zero and precedes two. In mathematics it is the multiplicative identity; multiplying any number by one leaves it unchanged. It is also the first natural number in most definitions and the smallest positive integer. By standard convention, one is neither prime nor composite because its only positive divisor is itself.

One appears in many numeral systems: Roman numerals use I, binary uses 1, and other bases have a single-digit representation for the value one. It is the first term of the natural numbers and the first triangular number; it serves as the initial element in many sequences and in counting.

In language and culture, the word one often connotes unity, indivisibility, or primary status. In philosophy, discussions of the One appear in monism and in conceptions of a single organizing principle. In religion the term is linked to monotheistic ideas. The notion also appears in music as the unison and in literature as a motif of wholeness.

In practical terms, one is used for counting items, identifying the first position, and representing truth in many computational and logical systems, where 1 denotes true and 0 denotes false. The concept of one thus intersects mathematics, language, philosophy, and culture, serving as a foundational element across disciplines.