The number 21015
21015 is a composite number with 12 divisors. Its prime factorisation is × 5 × 467. Divisors (12): 1, 3, 5, 9, 15, 45, 467, 1401, 2335, 4203, 7005, 21015.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21015: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 9.
- 2
21015 is composite. Its prime factorisation is
- 3
The divisors add up to 36504; without 21015 itself that is 15489, so 21015 is deficient (15489 is less than 21015). Euler's totient φ(21015) = 11184 numbers up to 21015 share no factor with it.
- 4
The digits of 21015 add up to 9, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21015 = 3^{2} \times 5 \times 467 \]21015 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 36504 |
| Euler totient φ(n) | 11184 |
| Square | 441630225 |
| Cube | 9280859178375 |
| Square root | 144.965513 (= 3√2335) |
| Digit sum / digital root | 9 / 9 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1015 × |
21015 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and fifteen |
| Binary (base 2) | 101001000010111 |
| Octal (base 8) | 51027 |
| Hexadecimal (base 16) | 5217 |
| Base 3 | 1001211100 |
| As time | 21015 seconds = 5 h 50 min 15 s |
Is 21015 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 (21015 ÷ 3 = 7005) | 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 (21015 ÷ 5 = 4203) | 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 1) | 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 | Yes (21015 ÷ 9 = 2335) | 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 5) | 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 21015 a prime number?
No. 21015 = × 5 × 467, so it is divisible by 3.
What are the factors of 21015?
1, 3, 5, 9, 15, 45, 467, 1401, 2335, 4203, 7005, 21015.
What is 21015 in binary?
101001000010111 (hexadecimal 5217, octal 51027).
What is the square root of 21015?
About 144.9655, exactly 3√2335.
Is 21015 divisible by 3?
Yes. Its digits add up to 9, a multiple of 3.
What is special about the number 21015?
21015 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 9.