21

Previous number

20

Next number

22

Sum of digits

3

Divisors of 21

Number of divisors

4

Sum of divisors

32

Factorization

21 = 3 × 7

Prime factors of 21

Factor Count
3 1
7 1

Square of 21

441

Cube of 21

9261

Square root of 21

4.58257569495583982899233888019808...

Cube root of 21

2.75892417638112030786601280851755...

21th triangle number

231

Reciprocal of 21

0.0476190476190476

Binary of 21

10101

Number of digits of 21 in base 2

5

Octal of 21

25

Hexadecimal of 21

15

Prime number No
Hexagonal number No
Perfect number No
Deficient number No
Abundant number No
Mersenne number No
Harshad number Yes
Harmonic divisor number No

Quadratic residues of 21

QR21 (sequence)

21th composite number

33

Euler's totient function of 21

12

Carmichael function of 21

6

Möbius function of 21

1

Properties of 21

Properties of the number 21: 21 has 4 divisors. The divisors of 21 are 1, 3, 7, 21 and the sum of them is 32. The factorization of 21 is 3 × 7. The square and cube of 21 are 441 and 9261 respectively. The square root and cube root of 21 are 4.58257569495583982899233888019808... and 2.75892417638112030786601280851755.... The binary, octal, hexadecimal of 21 are 10101, 25, 15. 21 is not a prime number, not hexagonal number, not perfect number, not deficient number, not Mersenne number, not Mersenne number, Harshad number, not harmonic divisor number.

sin 21

0.83665563853605595667772831802722...

cos 21

-0.54772926022426848824409262306290...

tan 21

-1.52749852763660309840076934051467...

sin 21°

0.35836794954530026835470835067099...

cos 21°

0.93358042649720174299687869279296...

tan 21°

0.38386403503541577375557380946702...

log 21

3.04452243772342301397770825133193...

log10 21

1.32221929473391930365266944136238...

log2 21

4.39231742277876069380226908833720...

Related pairs