Number 21

Interestingness: 10 · Rank #241 of 1000

Visual representations

Binary image (n×n bits)
Element Sc – Scandium
Triangular · P3(6) = 21
Octogonal · P8(3) = 21
37
Prime factorization

Representations of 21

Greek numeral
καʹ
Sanskrit numeral
२१
Arabic numeral
٢١
Roman numeral
XXI
Maya numeral
●
●
Chinese numeral
二十一
Hebrew numeral
כא
Egyptian numeral
𓎆𓎆
𓏹
Morse code
..---.----

21 in different numeral systems

Binary
10101
Base-3
210
Base-4
111
Base-5
41
Base-6
33
Base-7
30
Base-8
25
Duodecimal
19
Hex
15
Vigesimal
11
Base-24
l
Base-36
l
Negabinary
10101

Factorization

Prime factors: 3, 7
Divisors: 1, 3, 7, 21
Sum of divisors other than 21: 11
Product of prime factors: 21 = 3 × 7

Number-theory characteristics (9)

Triangular Octogonal Difference of 2 squares Odious number One O Odd Fibonacci Composite Deficient

Base-10 digit properties (1)

These depend on the decimal representation of the number.

Harshad

Related primes

Number 21 prime
Prime number before 21
Prime number after 21