The number 815
815 is a composite number with 4 divisors. Its prime factorisation is 5 × 163. Divisors (4): 1, 5, 163, 815.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 815: a semiprime: 5 × 163, the product of two primes.
- 2
815 is composite. Its prime factorisation is
- 3
The divisors add up to 984; without 815 itself that is 169, so 815 is deficient (169 is less than 815). Euler's totient φ(815) = 648 numbers up to 815 share no factor with it.
- 4
The digits of 815 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 134 steps to reach 1.
LaTeX source of the formulas on this page
\[ 815 = 5 \times 163 \]
815 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 984 |
| Euler totient φ(n) | 648 |
| Square | 664225 |
| Cube | 541343375 |
| Square root | 28.548205 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 134 |
| Scientific notation | 8.15 × |
815 in other forms
| Form | Value |
|---|---|
| In words | eight hundred and fifteen |
| Roman numerals | DCCCXV |
| Binary (base 2) | 1100101111 |
| Octal (base 8) | 1457 |
| Hexadecimal (base 16) | 32F |
| Base 3 | 1010012 |
| As time | 815 seconds = 13 min 35 s |
Is 815 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 | Yes (815 ÷ 5 = 163) | 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 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 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 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | 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 815 a prime number?
No. 815 = 5 × 163, so it is divisible by 5.
What are the factors of 815?
1, 5, 163, 815.
What is 815 in binary?
1100101111 (hexadecimal 32F, octal 1457).
What is the square root of 815?
About 28.5482.
What is 815 in Roman numerals?
DCCCXV.
Is 815 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 815?
815 is a semiprime: 5 × 163, the product of two primes.