The number 21315
21315 is a composite number with 24 divisors. Its prime factorisation is 3 × 5 × × 29. Divisors (24): 1, 3, 5, 7, 15, 21, 29, 35, 49, 87, 105, 145, 147, 203, 245, 435 … 21315.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21315 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21315 is composite. Its prime factorisation is
- 3
The divisors add up to 41040; without 21315 itself that is 19725, so 21315 is deficient (19725 is less than 21315). Euler's totient φ(21315) = 9408 numbers up to 21315 share no factor with it.
- 4
The digits of 21315 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 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21315 = 3 \times 5 \times 7^{2} \times 29 \]21315 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 41040 |
| Euler totient φ(n) | 9408 |
| Square | 454329225 |
| Cube | 9684027430875 |
| Square root | 145.996575 (= 7√435) |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.1315 × |
21315 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and fifteen |
| Binary (base 2) | 101001101000011 |
| Octal (base 8) | 51503 |
| Hexadecimal (base 16) | 5343 |
| Base 3 | 1002020110 |
| As time | 21315 seconds = 5 h 55 min 15 s |
Is 21315 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 (21315 ÷ 3 = 7105) | 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 (21315 ÷ 5 = 4263) | 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 | Yes (21315 ÷ 7 = 3045) | 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 | No (remainder 3) | 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 8) | 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 21315 a prime number?
No. 21315 = 3 × 5 × × 29, so it is divisible by 3.
What are the factors of 21315?
1, 3, 5, 7, 15, 21, 29, 35, 49, 87, 105, 145, 147, 203, 245, 435, 609, 735, 1015, 1421, 3045, 4263, 7105, 21315.
What is 21315 in binary?
101001101000011 (hexadecimal 5343, octal 51503).
What is the square root of 21315?
About 145.9966, exactly 7√435.
Is 21315 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 21315?
It is a composite number with 24 divisors.