1 (number) facts for kids
Quick facts for kids



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  1_{2}  
Ternary  1_{3}  
Quaternary  1_{4}  
Quinary  1_{5}  
Senary  1_{6}  
Octal  1_{8}  
Duodecimal  1_{12}  
Hexadecimal  1_{16}  
Vigesimal  1_{20}  
Base 36  1_{36}  
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 
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 (bellybutton). 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
Images for kids

The 24hour tower clock in Venice, using J as a symbol for 1
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1 (number) Facts for Kids. Kiddle Encyclopedia.