The number 21007
21007 is a composite number with 4 divisors. Its prime factorisation is 7 × 3001. Divisors (4): 1, 7, 3001, 21007.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21007: a semiprime: 7 × 3001, the product of two primes.
- 2
21007 is composite. Its prime factorisation is
- 3
The divisors add up to 24016; without 21007 itself that is 3009, so 21007 is deficient (3009 is less than 21007). Euler's totient φ(21007) = 18000 numbers up to 21007 share no factor with it.
- 4
The digits of 21007 add up to 10, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 131 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21007 = 7 \times 3001 \]
21007 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 24016 |
| Euler totient φ(n) | 18000 |
| Square | 441294049 |
| Cube | 9270264087343 |
| Square root | 144.937918 |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 131 |
| Scientific notation | 2.1007 × |
21007 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and seven |
| Binary (base 2) | 101001000001111 |
| Octal (base 8) | 51017 |
| Hexadecimal (base 16) | 520F |
| Base 3 | 1001211001 |
| As time | 21007 seconds = 5 h 50 min 7 s |
Is 21007 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 | No (remainder 1) | 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 | No (remainder 2) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21007 ÷ 7 = 3001) | 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 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 7) | 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 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21007 a prime number?
No. 21007 = 7 × 3001, so it is divisible by 7.
What are the factors of 21007?
1, 7, 3001, 21007.
What is 21007 in binary?
101001000001111 (hexadecimal 520F, octal 51017).
What is the square root of 21007?
About 144.9379.
Is 21007 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 21007?
21007 is a semiprime: 7 × 3001, the product of two primes.