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1 (one) is a positive integer following 0 and preceding 2. Its ordinal form is written "1st" or "first".

## Properties

1 is the first natural number. 1 is odd, and it's the only natural number that is neither prime nor composite.

1 is a triangular number, tetrahedral number, pentatope number, etc. It's also a square number, cubic number, etc.

1 is the multiplicative identity, meaning that $$a = a \times 1$$ for all $$a$$. In fact, $$a \underbrace{\uparrow\uparrow\ldots\uparrow\uparrow}_n 1 = a$$ (arrow notation) for all $$n,a \geq 0$$, so 1 is a sort of identity for all the hyper operators beyond addition. Furthermore, for all $$n,a > 0$$, $$a \underbrace{\uparrow\uparrow\ldots\uparrow\uparrow}_n 0 = 1$$ and $$1 \uparrow\uparrow\ldots\uparrow\uparrow n$$. 1 appears frequently as a "default" argument in googological notations, such as BEAF, chained arrow notation, and hyper-E notation.

All natural numbers are just strings of 1's added together. For example, 1,000,000 is a string of 1 million 1's added together.

1 is the only odd practical number.

1 is the only known odd multiperfect number.

The base one numbering system is called unary, as demonstrated by the video below:

## In other languages

Language Name
Afrikaans een
Albanian një
Amharic አንድ
Arabic واحد
Armenian մեկը
Azerbaijani bir
Bangla এক
Basque bat
Belarusian адзін
Bosnian, Croatian jedan
Bulgarian един (edin
Burmese တစ်
Catalan, French un
Chinese 一 (yī)
Czech, Slovak, Polish jeden
German eins
Italic, Spanish uno
Japanese いち (ichi)
Latvian viens
Macedonian, eден (eden)
Russian один (odin)
Serbian jедан (jedan)
Slovenian ena
Ukrainian oдин (odyn)
Zulu eyodwa

## In googology

Sbiis Saibian argued that all numbers larger than 1 should be called "large numbers," because the reciprocals of large numbers are small.[1] The large numbers and small numbers are "mirrored" about 1, so it makes sense to say that 1 is the threshold of largeness. A number like 1 + 1/googol could be called a "very small large number." The smallest large number is a logical impossibility, of course.

1 was also the first number by Adam Elga in the Big Number Duel.

1 can be named garone, fzone, fugaone, megafugaone, or boogaone with the gar-, fz-, fuga-, megafuga-, and booga- prefixes respectively.

## As a cash denomination

Some currencies, such as the Ghanaian cedi and the United States dollar, have banknotes with this number in the denomination. Likewise, some currencies, such as the euro and the pound sterling, have coins with this number in the denomination.

## Sources

1. Saibian, SbiisVery Small Very Large Numbers. Retrieved January 2013.