1 (number) facts for kids

Quick facts for kids ← 0 1 2 →
−1 0 1 2 3 4 5 6 7 8 9 → ← 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
Senary	16
Octal	18
Duodecimal	112
Hexadecimal	116
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

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.

Related pages

• Zero

See also

In Spanish: Uno para niños