Number 1: Natural number

The Roman numeral for one is I.

← 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
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

In mathematics, 1 is the multiplicative identity. It is sometimes called the "unity". It is also the only number for which these special facts are true:

• Any number ${\displaystyle n}$  multiplied by 1 equals that number: ${\displaystyle n\times 1=n}$ . For example, ${\displaystyle 7\times 1=7}$ .
• Any number ${\displaystyle n}$  divided by 1 equals that number: ${\displaystyle n/1=n}$ . For example, ${\displaystyle 7/1=7}$ .
• Any number ${\displaystyle n}$ , except 0, divided by itself equals 1: ${\displaystyle n/n=1}$ . For example: ${\displaystyle 7/7=1}$ .
• 1 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.

The number one is important for computer science, because the binary numeral system uses only 1s and 0s to represent numbers. In machine code and many programming languages, one means "true" (or "yes") and zero means "false" (or "no").

• 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.

• Zero
• Mathematical constant