The number 399
399 is a composite number with 8 divisors. Its prime factorisation is 3 × 7 × 19. Divisors (8): 1, 3, 7, 19, 21, 57, 133, 399.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 399: a Harshad number: divisible by its digit sum 21.
- 2
399 is composite. Its prime factorisation is
- 3
The divisors add up to 640; without 399 itself that is 241, so 399 is deficient (241 is less than 399). Euler's totient φ(399) = 216 numbers up to 399 share no factor with it.
- 4
The digits of 399 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 120 steps to reach 1.
LaTeX source of the formulas on this page
\[ 399 = 3 \times 7 \times 19 \]
399 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 640 |
| Euler totient φ(n) | 216 |
| Square | 159201 |
| Cube | 63521199 |
| Square root | 19.974984 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 120 |
| Scientific notation | 3.99 × |
399 in other forms
| Form | Value |
|---|---|
| In words | three hundred and ninety-nine |
| Roman numerals | CCCXCIX |
| Binary (base 2) | 110001111 |
| Octal (base 8) | 617 |
| Hexadecimal (base 16) | 18F |
| Base 3 | 112210 |
| As time | 399 seconds = 6 min 39 s |
Is 399 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 (399 ÷ 3 = 133) | 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 (399 ÷ 7 = 57) | 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 3) | 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 3) | 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 399 a prime number?
No. 399 = 3 × 7 × 19, so it is divisible by 3.
What are the factors of 399?
1, 3, 7, 19, 21, 57, 133, 399.
What is 399 in binary?
110001111 (hexadecimal 18F, octal 617).
What is the square root of 399?
About 19.9750.
What is 399 in Roman numerals?
CCCXCIX.
Is 399 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 399?
399 is a Harshad number: divisible by its digit sum 21.