The number 1381
1381 is the 221st prime number. Its only divisors are 1 and 1381.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1381: the 221st prime number.
- 2
1381 is prime, so its only factors are 1 and 1381. It is the 221st prime; the next prime is 1399 and the one before is 1373.
- 3
The divisors add up to 1382; without 1381 itself that is 1, so 1381 is deficient (1 is less than 1381). Euler's totient φ(1381) = 1380 numbers up to 1381 share no factor with it.
- 4
The digits of 1381 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 127 steps to reach 1.
1381 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 1382 |
| Euler totient φ(n) | 1380 |
| Square | 1907161 |
| Cube | 2633789341 |
| Square root | 37.161808 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 127 |
| Scientific notation | 1.381 × |
1381 in other forms
| Form | Value |
|---|---|
| In words | one thousand three hundred and eighty-one |
| Roman numerals | MCCCLXXXI |
| Binary (base 2) | 10101100101 |
| Octal (base 8) | 2545 |
| Hexadecimal (base 16) | 565 |
| Base 3 | 1220011 |
| As time | 1381 seconds = 23 min 1 s |
Is 1381 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 1) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 2) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 4) | 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 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1381 a prime number?
Yes. 1381 is divisible only by 1 and itself.
What are the factors of 1381?
1, 1381.
What is 1381 in binary?
10101100101 (hexadecimal 565, octal 2545).
What is the square root of 1381?
About 37.1618.
What is 1381 in Roman numerals?
MCCCLXXXI.
Is 1381 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 1381?
1381 is the 221st prime number.