The number 921
921 is a composite number with 4 divisors. Its prime factorisation is 3 × 307. Divisors (4): 1, 3, 307, 921.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 921: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 307, the product of two primes.
- 2
921 is composite. Its prime factorisation is
- 3
The divisors add up to 1232; without 921 itself that is 311, so 921 is deficient (311 is less than 921). Euler's totient φ(921) = 612 numbers up to 921 share no factor with it.
- 4
The digits of 921 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 129 steps to reach 1.
LaTeX source of the formulas on this page
\[ 921 = 3 \times 307 \]
921 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 1232 |
| Euler totient φ(n) | 612 |
| Square | 848241 |
| Cube | 781229961 |
| Square root | 30.347982 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 129 |
| Scientific notation | 9.21 × |
921 in other forms
| Form | Value |
|---|---|
| In words | nine hundred and twenty-one |
| Roman numerals | CMXXI |
| Binary (base 2) | 1110011001 |
| Octal (base 8) | 1631 |
| Hexadecimal (base 16) | 399 |
| Base 3 | 1021010 |
| As time | 921 seconds = 15 min 21 s |
Is 921 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 (921 ÷ 3 = 307) | 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 4) | 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 1) | 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 8) | 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 921 a prime number?
No. 921 = 3 × 307, so it is divisible by 3.
What are the factors of 921?
1, 3, 307, 921.
What is 921 in binary?
1110011001 (hexadecimal 399, octal 1631).
What is the square root of 921?
About 30.3480.
What is 921 in Roman numerals?
CMXXI.
Is 921 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 921?
921 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 307, the product of two primes.