The number 21399
21399 is a composite number with 8 divisors. Its prime factorisation is 3 × 7 × 1019. Divisors (8): 1, 3, 7, 21, 1019, 3057, 7133, 21399.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21399: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21399 is composite. Its prime factorisation is
- 3
The divisors add up to 32640; without 21399 itself that is 11241, so 21399 is deficient (11241 is less than 21399). Euler's totient φ(21399) = 12216 numbers up to 21399 share no factor with it.
- 4
The digits of 21399 add up to 24, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 48 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21399 = 3 \times 7 \times 1019 \]
21399 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 32640 |
| Euler totient φ(n) | 12216 |
| Square | 457917201 |
| Cube | 9798970184199 |
| Square root | 146.283970 |
| Digit sum / digital root | 24 / 6 |
| Collatz steps to 1 | 48 |
| Scientific notation | 2.1399 × |
21399 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and ninety-nine |
| Binary (base 2) | 101001110010111 |
| Octal (base 8) | 51627 |
| Hexadecimal (base 16) | 5397 |
| Base 3 | 1002100120 |
| As time | 21399 seconds = 5 h 56 min 39 s |
Is 21399 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21399 ÷ 3 = 7133) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 4) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21399 ÷ 7 = 3057) | 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 7) | 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 | No (remainder 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 4) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21399 a prime number?
No. 21399 = 3 × 7 × 1019, so it is divisible by 3.
What are the factors of 21399?
1, 3, 7, 21, 1019, 3057, 7133, 21399.
What is 21399 in binary?
101001110010111 (hexadecimal 5397, octal 51627).
What is the square root of 21399?
About 146.2840.
Is 21399 divisible by 3?
Yes. Its digits add up to 24, a multiple of 3.
What is special about the number 21399?
21399 is a happy number: repeatedly adding the squares of its digits reaches 1.