# 1 (number) facts for kids

Kids Encyclopedia Facts
Quick facts for kids
 ← 0 1 2 →
Cardinal one
Ordinal 1st
(first)
Numeral system unary
Factorization 1
Divisors 1
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
Vigesimal 120
Base 36 136
Greek numeral α'
Persian ١ - یک
Arabic ١
Urdu
Ge'ez
Bengali & Assamese
Chinese numeral 一，弌，壹
Korean 일, 하나
Devanāgarī
Telugu
Tamil
Hebrew א (alef)
Khmer
Thai
Malayalam
Chinese hand sign

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.

## Mathematics

In mathematics, 1 is the multiplicative identity of common numbers. 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 × 1 = n. For example, 7 × 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 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 many programming languages, one means true and zero means false.

## Images for kids

1 (number) Facts for Kids. Kiddle Encyclopedia.