The number 81315
81315 is a composite number with 24 divisors. Its prime factorisation is × 5 × 13 × 139. Divisors (24): 1, 3, 5, 9, 13, 15, 39, 45, 65, 117, 139, 195, 417, 585, 695, 1251 … 81315.
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How to work it out
- 1
What is special about 81315: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
81315 is composite. Its prime factorisation is
- 3
The divisors add up to 152880; without 81315 itself that is 71565, so 81315 is deficient (71565 is less than 81315). Euler's totient φ(81315) = 39744 numbers up to 81315 share no factor with it.
- 4
The digits of 81315 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 76 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81315 = 3^{2} \times 5 \times 13 \times 139 \]81315 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 152880 |
| Euler totient φ(n) | 39744 |
| Square | 6612129225 |
| Cube | 537665287930875 |
| Square root | 285.157851 (= 3√9035) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 76 |
| Scientific notation | 8.1315 × |
81315 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand three hundred and fifteen |
| Binary (base 2) | 10011110110100011 |
| Octal (base 8) | 236643 |
| Hexadecimal (base 16) | 13DA3 |
| Base 3 | 11010112200 |
| As time | 81315 seconds = 22 h 35 min 15 s |
Is 81315 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 (81315 ÷ 3 = 27105) | 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 (81315 ÷ 5 = 16263) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (81315 ÷ 9 = 9035) | 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 3) | 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 81315 a prime number?
No. 81315 = × 5 × 13 × 139, so it is divisible by 3.
What are the factors of 81315?
1, 3, 5, 9, 13, 15, 39, 45, 65, 117, 139, 195, 417, 585, 695, 1251, 1807, 2085, 5421, 6255, 9035, 16263, 27105, 81315.
What is 81315 in binary?
10011110110100011 (hexadecimal 13DA3, octal 236643).
What is the square root of 81315?
About 285.1579, exactly 3√9035.
Is 81315 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 81315?
81315 is a happy number: repeatedly adding the squares of its digits reaches 1.