The number 1391
1391 is a composite number with 4 divisors. Its prime factorisation is 13 × 107. Divisors (4): 1, 13, 107, 1391.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1391: a semiprime: 13 × 107, the product of two primes.
- 2
1391 is composite. Its prime factorisation is
- 3
The divisors add up to 1512; without 1391 itself that is 121, so 1391 is deficient (121 is less than 1391). Euler's totient φ(1391) = 1272 numbers up to 1391 share no factor with it.
- 4
The digits of 1391 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 114 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1391 = 13 \times 107 \]
1391 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 1512 |
| Euler totient φ(n) | 1272 |
| Square | 1934881 |
| Cube | 2691419471 |
| Square root | 37.296112 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 114 |
| Scientific notation | 1.391 × |
1391 in other forms
| Form | Value |
|---|---|
| In words | one thousand three hundred and ninety-one |
| Roman numerals | MCCCXCI |
| Binary (base 2) | 10101101111 |
| Octal (base 8) | 2557 |
| Hexadecimal (base 16) | 56F |
| Base 3 | 1220112 |
| As time | 1391 seconds = 23 min 11 s |
Is 1391 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 | No (remainder 2) | 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 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 5) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1391 a prime number?
No. 1391 = 13 × 107, so it is divisible by 13.
What are the factors of 1391?
1, 13, 107, 1391.
What is 1391 in binary?
10101101111 (hexadecimal 56F, octal 2557).
What is the square root of 1391?
About 37.2961.
What is 1391 in Roman numerals?
MCCCXCI.
Is 1391 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 1391?
1391 is a semiprime: 13 × 107, the product of two primes.