The number 21390
21390 is a composite number with 32 divisors. Its prime factorisation is 2 × 3 × 5 × 23 × 31. Divisors (32): 1, 2, 3, 5, 6, 10, 15, 23, 30, 31, 46, 62, 69, 93, 115, 138 … 21390.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21390: a Harshad number: divisible by its digit sum 15.
- 2
21390 is composite. Its prime factorisation is
- 3
The divisors add up to 55296; without 21390 itself that is 33906, so 21390 is abundant (33906 is more than 21390). Euler's totient φ(21390) = 5280 numbers up to 21390 share no factor with it.
- 4
The digits of 21390 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21390 = 2 \times 3 \times 5 \times 23 \times 31 \]
21390 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 32 |
| Sum of divisors | 55296 |
| Euler totient φ(n) | 5280 |
| Square | 457532100 |
| Cube | 9786611619000 |
| Square root | 146.253205 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 74 |
| Scientific notation | 2.139 × |
21390 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and ninety |
| Binary (base 2) | 101001110001110 |
| Octal (base 8) | 51616 |
| Hexadecimal (base 16) | 538E |
| Base 3 | 1002100020 |
| As time | 21390 seconds = 5 h 56 min 30 s |
Is 21390 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21390 ÷ 2 = 10695) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21390 ÷ 3 = 7130) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 2) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21390 ÷ 5 = 4278) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21390 ÷ 6 = 3565) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 5) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 6) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21390 ÷ 10 = 2139) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 6) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21390 a prime number?
No. 21390 = 2 × 3 × 5 × 23 × 31, so it is divisible by 2.
What are the factors of 21390?
1, 2, 3, 5, 6, 10, 15, 23, 30, 31, 46, 62, 69, 93, 115, 138, 155, 186, 230, 310, 345, 465, 690, 713, 930, 1426, 2139, 3565, 4278, 7130, 10695, 21390.
What is 21390 in binary?
101001110001110 (hexadecimal 538E, octal 51616).
What is the square root of 21390?
About 146.2532.
Is 21390 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21390?
21390 is a Harshad number: divisible by its digit sum 15.