The number 1815
1815 is a composite number with 12 divisors. Its prime factorisation is 3 × 5 × . Divisors (12): 1, 3, 5, 11, 15, 33, 55, 121, 165, 363, 605, 1815.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1815: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 15.
- 2
1815 is composite. Its prime factorisation is
- 3
The divisors add up to 3192; without 1815 itself that is 1377, so 1815 is deficient (1377 is less than 1815). Euler's totient φ(1815) = 880 numbers up to 1815 share no factor with it.
- 4
The digits of 1815 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 55 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1815 = 3 \times 5 \times 11^{2} \]1815 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 3192 |
| Euler totient φ(n) | 880 |
| Square | 3294225 |
| Cube | 5979018375 |
| Square root | 42.602817 (= 11√15) |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 55 |
| Scientific notation | 1.815 × |
1815 in other forms
| Form | Value |
|---|---|
| In words | one thousand eight hundred and fifteen |
| Roman numerals | MDCCCXV |
| Binary (base 2) | 11100010111 |
| Octal (base 8) | 3427 |
| Hexadecimal (base 16) | 717 |
| Base 3 | 2111020 |
| As time | 1815 seconds = 30 min 15 s |
Is 1815 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 (1815 ÷ 3 = 605) | 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 (1815 ÷ 5 = 363) | 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 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | 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 | Yes (1815 ÷ 11 = 165) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1815 a prime number?
No. 1815 = 3 × 5 × , so it is divisible by 3.
What are the factors of 1815?
1, 3, 5, 11, 15, 33, 55, 121, 165, 363, 605, 1815.
What is 1815 in binary?
11100010111 (hexadecimal 717, octal 3427).
What is the square root of 1815?
About 42.6028, exactly 11√15.
What is 1815 in Roman numerals?
MDCCCXV.
Is 1815 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 1815?
1815 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 15.