# 1 (number)

natural number
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One (1) is a natural number after zero and before 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 also the only number for which these special facts are true.

• Any number n multiplied by 1 equals that number: n × 1 = n, example 7 × 1 = 7.
• Any number n divided by 1 equals that number: n / 1 = n, example: 7 / 1 = 7.
• Any number n, other than 0, divided by itself always equals 1: n / n = 1, example: 7 / 7 = 1.
• 1 cannot be divided with any other number so that the result is a natural number.

In mathematics 0.999... is a repeating decimal that is mathematically 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. In machine code, and in many programming languages, one means true and zero means false.

## 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 and best. In Poland, one is also the lowest grade, but the highest is six.
• In numerology, the number one is a symbol for everything (unity), the beginning, and God.