21
Number 21 properties
- 21 is an odd number.
- 21 is triangular and equals T6.
- 21 is Fibonacci number #8.
- 21 is a Harshad number, which means it is divisible by the sum of its digits (21 = 3, and 21 is divisible by 3).
Number 21 - properties and curiosities
21 (number)
Prime factorization
Prime factorization of 21: 3 × 7.
Divisors
Divisor count: 4
1, 3, 7, 21
Factors of 21 are: 1, 3, 7, 21.
Representations
In octal, 21 is represented as 25.
In binary, 21 is represented as 10101.
In hex, 21 is represented as 15.
Roman numeral: XXI
Curiosities
- 21 appears in the Fibonacci sequence, where each number is the sum of the previous two.
- 21 is divisible by the sum of its digits.
Related numbers
Quick answers
Is 21 prime?
No, 21 is not prime.
What are the factors of 21?
1, 3, 7, 21
What is 21 in binary?
10101