The number 381
381 is a binary palindrome (101111101). Its prime factorisation is 3 × 127. Divisors (4): 1, 3, 127, 381.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 381: a binary palindrome (101111101); a semiprime: 3 × 127, the product of two primes.
- 2
381 is composite. Its prime factorisation is
- 3
The divisors add up to 512; without 381 itself that is 131, so 381 is deficient (131 is less than 381). Euler's totient φ(381) = 252 numbers up to 381 share no factor with it.
- 4
The digits of 381 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 107 steps to reach 1.
LaTeX source of the formulas on this page
\[ 381 = 3 \times 127 \]
381 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 512 |
| Euler totient φ(n) | 252 |
| Square | 145161 |
| Cube | 55306341 |
| Square root | 19.519221 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 107 |
| Scientific notation | 3.81 × |
381 in other forms
| Form | Value |
|---|---|
| In words | three hundred and eighty-one |
| Roman numerals | CCCLXXXI |
| Binary (base 2) | 101111101 |
| Octal (base 8) | 575 |
| Hexadecimal (base 16) | 17D |
| Base 3 | 112010 |
| As time | 381 seconds = 6 min 21 s |
Is 381 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 (381 ÷ 3 = 127) | 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 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 3) | 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 3) | 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 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 381 a prime number?
No. 381 = 3 × 127, so it is divisible by 3.
What are the factors of 381?
1, 3, 127, 381.
What is 381 in binary?
101111101 (hexadecimal 17D, octal 575).
What is the square root of 381?
About 19.5192.
What is 381 in Roman numerals?
CCCLXXXI.
Is 381 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 381?
381 is a binary palindrome (101111101); a semiprime: 3 × 127, the product of two primes.