Twenty-one

This article is about the number twenty-one . For the year AD 21 , see 21 , for additional meanings see 21 (disambiguation) .

Twenty-one
21st
presentation
Roman	XXI
dual	1 0101
Octal	25th
Duodecimal	19th
Hexadecimal	15th
Morse code	· · - - - · - - - -
Chinese	二十 一
Mathematical properties
sign	positive
parity	odd
Factorization	${\displaystyle 3\cdot 7}$
Divider	1, 3, 7, 21

The twenty-one (21) is the natural number between twenty and twenty-two . It's odd .

Math

• Twenty-one is the number between thirteen and thirty-four in the Fibonacci sequence .
• 21 is a triangular number : ${\displaystyle 21=\sum _{i=1}^{6}i}$
• 21 is the smallest odd group order of a non-Abelian group .
• Twenty-one is the smallest positive natural number for which squares exist in pairs with different positive edge lengths, which can be put together to form a square, see squaring of the square . ${\displaystyle n}$ ${\displaystyle n}$

Culture and society

• 21 is an American film drama from the year 2008 .
• 21 is the second album by the British singer Adele .
• 21 is the twenty-first studio album by the German power metal band Rage .
• 21 is the numeric code for the Blue Angels MC motorcycle club
• Quiz 21 is a quiz broadcast format developed by NBC as "twenty-one".
• 21 Savage is a British rapper

Web links

Commons : Twenty-one  - collection of images, videos, and audio files

Wiktionary: twenty-one  - explanations of meanings, word origins, synonyms, translations