The number 21008
21008 is a composite number with 20 divisors. Its prime factorisation is × 13 × 101. Divisors (20): 1, 2, 4, 8, 13, 16, 26, 52, 101, 104, 202, 208, 404, 808, 1313, 1616 … 21008.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21008 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21008 is composite. Its prime factorisation is
- 3
The divisors add up to 44268; without 21008 itself that is 23260, so 21008 is abundant (23260 is more than 21008). Euler's totient φ(21008) = 9600 numbers up to 21008 share no factor with it.
- 4
The digits of 21008 add up to 11, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 30 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21008 = 2^{4} \times 13 \times 101 \]21008 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 20 |
| Sum of divisors | 44268 |
| Euler totient φ(n) | 9600 |
| Square | 441336064 |
| Cube | 9271588032512 |
| Square root | 144.941367 (= 4√1313) |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 30 |
| Scientific notation | 2.1008 × |
21008 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and eight |
| Binary (base 2) | 101001000010000 |
| Octal (base 8) | 51020 |
| Hexadecimal (base 16) | 5210 |
| Base 3 | 1001211002 |
| As time | 21008 seconds = 5 h 50 min 8 s |
Is 21008 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21008 ÷ 2 = 10504) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21008 ÷ 4 = 5252) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 3) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 2) | 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 | Yes (21008 ÷ 8 = 2626) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 8) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21008 a prime number?
No. 21008 = × 13 × 101, so it is divisible by 2.
What are the factors of 21008?
1, 2, 4, 8, 13, 16, 26, 52, 101, 104, 202, 208, 404, 808, 1313, 1616, 2626, 5252, 10504, 21008.
What is 21008 in binary?
101001000010000 (hexadecimal 5210, octal 51020).
What is the square root of 21008?
About 144.9414, exactly 4√1313.
Is 21008 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 21008?
It is a composite number with 20 divisors.