21 (number)
21 (twenty-one) is a number. It comes between twenty and twenty-two, and is an odd number. It is divisible by 1, 3, 7, and 21.
| ||||
|---|---|---|---|---|
| Cardinal | twenty-one | |||
| Ordinal | 21st (twenty-first) | |||
| Factorization | 3 · 7 | |||
| Roman numeral | XXI | |||
| Binary | 101012 | |||
| Ternary | 2103 | |||
| Quaternary | 1114 | |||
| Quinary | 415 | |||
| Senary | 336 | |||
| Octal | 258 | |||
| Duodecimal | 1912 | |||
| Hexadecimal | 1516 | |||
| Vigesimal | 1120 | |||
| Base 36 | L36 | |||
Twenty-one is also a name of a popular card game and is the age at which people in the United States can buy alcoholic drinks.
In Roman numerals, 21 is written as XXI.
In Greek numerals 21 is written as κα
21 (number) Media
The minimum number of squares needed to square the square (using different edge-lengths) is 21.
Building called "21" in Zlín, Czech Republic.
Detail of the building entrance.
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