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1 (number) facts for kids

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0 1 2
−1 0 1 2 3 4 5 6 7 8 9
Cardinal one
Ordinal 1st
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
Hexadecimal 116
Vigesimal 120
Base 36 136
Greek numeral α'
Persian ١ - یک
Arabic ١
Bengali & Assamese
Chinese numeral 一,弌,壹
Korean 일, 하나
Hebrew א (alef)
Chinese hand sign
Pronunciation of the number 1.

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.


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.

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 the 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.

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