# 1 (number)

natural number

One (1) is the first natural number, followed by two. It represents a single item. A human typically has one head, nose, mouth, and navel (belly-button). The Roman numeral for one is I.

 ← 0 1 2 →
Cardinalone
Ordinal1st
(first)
Numeral systemunary
Factorization1
Divisors1
Greek numeralΑ´
Roman numeralI
Roman numeral (unicode)Ⅰ, ⅰ
Greek prefixmono- /haplo-
Latin prefixuni-
Binary12
Ternary13
Quaternary14
Quinary15
Senary16
Octal18
Duodecimal112
Vigesimal120
Base 36136
Greek numeralα'
Persian١ - یک
Arabic١
Urdu Ge'ez
Bengali & Assamese
Chinese numeral一，弌，壹
Korean일, 하나
Devanāgarī
Telugu
Tamil
Hebrewא (alef)
Khmer
Thai
Malayalam
counting rod𝍠
Pronunciation of the number 1.

## Mathematics

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 $n$  multiplied by 1 equals that number: $n\times 1=n$ . For example, $7\times 1=7$ .
• Any number $n$  divided by 1 equals that number: $n/1=n$ . For example, $7/1=7$ .
• Any number $n$ , other than 0, divided by itself always equals 1: $n/n=1$ . For example: $7/7=1$ .
• 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.

## Computer science

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").

## 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.