The number 813
813 is a composite number with 4 divisors. Its prime factorisation is 3 × 271. Divisors (4): 1, 3, 271, 813.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 813: a semiprime: 3 × 271, the product of two primes.
- 2
813 is composite. Its prime factorisation is
- 3
The divisors add up to 1088; without 813 itself that is 275, so 813 is deficient (275 is less than 813). Euler's totient φ(813) = 540 numbers up to 813 share no factor with it.
- 4
The digits of 813 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 41 steps to reach 1.
LaTeX source of the formulas on this page
\[ 813 = 3 \times 271 \]
813 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 1088 |
| Euler totient φ(n) | 540 |
| Square | 660969 |
| Cube | 537367797 |
| Square root | 28.513155 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 41 |
| Scientific notation | 8.13 × |
813 in other forms
| Form | Value |
|---|---|
| In words | eight hundred and thirteen |
| Roman numerals | DCCCXIII |
| Binary (base 2) | 1100101101 |
| Octal (base 8) | 1455 |
| Hexadecimal (base 16) | 32D |
| Base 3 | 1010010 |
| As time | 813 seconds = 13 min 33 s |
Is 813 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 (813 ÷ 3 = 271) | 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 3) | 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 1) | 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 3) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 10) | 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 813 a prime number?
No. 813 = 3 × 271, so it is divisible by 3.
What are the factors of 813?
1, 3, 271, 813.
What is 813 in binary?
1100101101 (hexadecimal 32D, octal 1455).
What is the square root of 813?
About 28.5132.
What is 813 in Roman numerals?
DCCCXIII.
Is 813 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 813?
813 is a semiprime: 3 × 271, the product of two primes.