21 Number Properties & Facts

Twenty-One

Primality

Prime Factorization of 21
31 × 71
Number of Divisors in 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

Numeric Bases

21 in Binary
0b10101
Base 2
21 in Octal
025
Base 8
21 in Hexadecimal
0x15
Base 16

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

Miscellaneous

Number of Significant Figures in 21
2
Hamming Weight of 21
3
Is 21 a Hamming (Regular) Number?
No
Is 21 a Humble Number?
Yes
Is 21 a Polygonal (s < 13) Number?
Triangular (6), Octagonal (3)
Is 21 a Happy Number?
No
Is 21 a Self Describing Number?
No
Is 21 a Palindrome?
No
Is 21 a Münchhausen Number?
No
Is 21 an Eban Number?
No
Is 21 a Pernicious Number?
Yes
Is 21 a Attractive Number?
Yes
Is 21 a Perfect Square?
No
Is 21 a Perfect Power?
No