The number 21615
21615 is a composite number with 16 divisors. Its prime factorisation is 3 × 5 × 11 × 131. Divisors (16): 1, 3, 5, 11, 15, 33, 55, 131, 165, 393, 655, 1441, 1965, 4323, 7205, 21615.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21615: a Harshad number: divisible by its digit sum 15.
- 2
21615 is composite. Its prime factorisation is
- 3
The divisors add up to 38016; without 21615 itself that is 16401, so 21615 is deficient (16401 is less than 21615). Euler's totient φ(21615) = 10400 numbers up to 21615 share no factor with it.
- 4
The digits of 21615 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 162 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21615 = 3 \times 5 \times 11 \times 131 \]
21615 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 38016 |
| Euler totient φ(n) | 10400 |
| Square | 467208225 |
| Cube | 10098705783375 |
| Square root | 147.020407 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 162 |
| Scientific notation | 2.1615 × |
21615 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand six hundred and fifteen |
| Binary (base 2) | 101010001101111 |
| Octal (base 8) | 52157 |
| Hexadecimal (base 16) | 546F |
| Base 3 | 1002122120 |
| As time | 21615 seconds = 6 h 0 min 15 s |
Is 21615 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 (21615 ÷ 3 = 7205) | 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 (21615 ÷ 5 = 4323) | 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 6) | 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 (21615 ÷ 11 = 1965) | 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 21615 a prime number?
No. 21615 = 3 × 5 × 11 × 131, so it is divisible by 3.
What are the factors of 21615?
1, 3, 5, 11, 15, 33, 55, 131, 165, 393, 655, 1441, 1965, 4323, 7205, 21615.
What is 21615 in binary?
101010001101111 (hexadecimal 546F, octal 52157).
What is the square root of 21615?
About 147.0204.
Is 21615 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21615?
21615 is a Harshad number: divisible by its digit sum 15.