1 (number)

One (1) is the first natural number, followed by two. The Roman numeral for one is I.

Babylonian number 1

← 0 1 2 →
-1 0 1 2 3 4 5 6 7 8 9 → List of numbers — Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	one, unit, unity
Ordinal	1st (first)
Numeral system	unary
Factorization	1
Divisors	1
Greek numeral	Α´
Roman numeral	I
Roman numeral (unicode)	Ⅰ, ⅰ
Greek prefix	mono- /haplo-
Latin prefix	uni-
Binary	12
Ternary	13
Quaternary	14
Quinary	15
Senary	16
Octal	18
Duodecimal	112
Hexadecimal	116
Vigesimal	120
Base 36	136
Greek numeral	α'
Persian	١ - یک
Arabic	١
Urdu
Ge'ez	፩
Bengali & Assamese	১
Chinese numeral	一，弌，壹
Korean	일, 하나
Devanāgarī	१
Telugu	೧
Tamil	௧
Kannada	೧
Hebrew	א (alef)
Khmer	១
Thai	๑
Malayalam	൧
Counting rod	𝍠

Chinese hand sign

Pronunciation of the number 1.

This article is about the number one. For the year, see 1.

Not to be confused with I.

Mathematics

In mathematics, the number one is the multiplicative identity.^[1] It is also the only number for which these special facts are true:

• Any number ${\displaystyle n}$ multiplied by one equals that number: ${\displaystyle n\times 1=n}$. For example, ${\displaystyle 7\times 1=7}$.
• Any number ${\displaystyle n}$ divided by one equals that number: ${\displaystyle n/1=n}$. For example, ${\displaystyle 7/1=7}$.
• Any number ${\displaystyle n}$, except zero, divided by itself equals one: ${\displaystyle n/n=1}$. For example: ${\displaystyle 7/7=1}$.
• One cannot be divided by any other number bigger than itself so that the result is a natural number.

In mathematics, 0.999... is a repeating decimal that is equal to 1. Many proofs have been made to show this is correct.^[2][3]

Computer science

One is important for computer science, because the binary numeral system uses only ones and zeroes to represent numbers. In machine code and many programming languages, one means "true" (or "yes") and zero means "false" (or "no").

Other meanings

• In Germany and Austria, one is the grade for "very good". It is the best grade of six possible grades in Germany, and the best of five possible grades in Austria. In the Netherlands, one is the lowest grade, and ten the highest. In Poland, one is also the lowest grade, and the highest is six.
• In numerology, the number one is a symbol for everything (unity), the beginning, and God.

Related pages

• Zero
• Mathematical constant