# 1 (number)

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File:En-us-One.ogg
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.

## Mathematics

In mathematics, 1 is also the only number for which these special facts are true.

• Any number n multiplied by 1 equals that number: n × 1 = n, example 7 × 1 = 7.
• Any number n divided by 1 equals that number: n / 1 = n, example: 7 / 1 = 7.
• Any number n, other than 0, divided by itself always equals 1: n / n = 1, 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 in 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 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.