21 Number Properties & Facts

Twenty-One

Primality

Prime Factorization of 21
31 × 71
Number of Divisors of 21
4
1, 3, 7, 21
1, 3, 7, 21
Is 21 Prime?
No

Trigonometry

Sine of 21
0.83665563853606
Cosecant: 1.1952348779359
Cosine of 21
-0.54772926022427
Secant: -1.825719516227
Tangent of 21
-1.5274985276366
Cotangent: -0.65466511548606

Functions

Square of 21
441
21 × 21 = 441
Square Root of 21
4.5825756949558
4.58257569495582 = 21
Natural Logarithm (ln) of 21
3.0445224377234
e3.0445224377234 = 21
Decimal Logarithm (log) of 21
1.3222192947339
101.3222192947339 = 21

Sequences

Is 21 a Fibonacci Number?
Yes: F8
Is 21 a Bell Number?
No
Is 21 a Catalan Number?
No
Is 21 a Factorial?
No
Is 21 a Perfect Number?
No

Translations

How do you say 21 in different languages?
Englishtwenty-one
españolveintiuno
françaisvingt-et-un
Deutschein­und­zwanzig
Nederlandseen­en­twintig
русскийдвадцать один
українськадвадцять один
Tiếng Việthai mươi mốt
العربيةواحد و عشرون
עבריתעשרים ואחת
हिन्दीइक्कीस
中文二十一
日本語二十一
한국어이십일
češtinadvacet jeden
hrvatskidvadeset i jedan
slovenčinadvadsať­jeden
polskidwadzieścia jeden
Türkçeyirmi bir
portuguêsvinte e um
italianovent­uno
svenskatjugo­ett
suomikaksi­kymmentä­yksi
norsktjue­én
Filipinodalawáng pû’t isá
Melayudua puluh satu
မြန်မာနှစ်ဆယ်တစ်
Indonesiadua puluh satu
Kiswahiliishirini na moja

Numeric Bases

21 in Binary (Base 2)
0b10101
One's Complement: 01010
Two's Complement: 01011
21 in Octal (Base 8)
025
21 in Hexadecimal (Base 16)
0x15

Miscellaneous

  • 21 is an odd number
  • 21 has 2 Significant Figures
  • The Hamming Weight of 21 is 3
  • 21 is not a Hamming (Regular) Number
  • 21 is a Humble Number
  • 21 is a Polygonal (s < 13) Number: Triangular (6), Octagonal (3)
  • 21 is not a Happy Number
  • 21 is not a Self Describing Number
  • 21 is not a Palindrome
  • 21 is not a Münchhausen Number
  • 21 is not an Eban Number
  • 21 is a Pernicious Number
  • 21 is an Attractive Number
  • 21 is not a Perfect Square
  • 21 is not a Perfect Power