1 (number)

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0 1 2
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 is I.

Mathematics[change | change source]

In mathematics, one is also the only number with this special fact: Any number multiplied by 1 equals that number. Then, the number 1 divides any number but it is not divided by any except itself. The number 1 divides any number to give that same number but it cannot be divided by any other number to give one as the answer. Let n be any number. Then n/1 = n but 1/n is never 1 (when n is not 1). Example: 7/1 = 7, but 1/7 is not 1 (it is 0.142857...).

Any number divided by itself always gives 1 as the answer. n/n = 1 (when n is not 0). Example: 7/7 = 1.

0.999... is a repeating decimal that is mathematically equal to 1. Many proofs have been made to show this is correct.

Computer science[change | change source]

The number one is important for computer science because it is, together with zero, a part of the binary numeral system. In machine code and in many programming languages, one means true and zero means false.

Other meanings[change | change source]

  • 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.