The number 21018
21018 is a composite number with 16 divisors. Its prime factorisation is 2 × 3 × 31 × 113. Divisors (16): 1, 2, 3, 6, 31, 62, 93, 113, 186, 226, 339, 678, 3503, 7006, 10509, 21018.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21018: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21018 is composite. Its prime factorisation is
- 3
The divisors add up to 43776; without 21018 itself that is 22758, so 21018 is abundant (22758 is more than 21018). Euler's totient φ(21018) = 6720 numbers up to 21018 share no factor with it.
- 4
The digits of 21018 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 30 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21018 = 2 \times 3 \times 31 \times 113 \]
21018 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 43776 |
| Euler totient φ(n) | 6720 |
| Square | 441756324 |
| Cube | 9284834417832 |
| Square root | 144.975860 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 30 |
| Scientific notation | 2.1018 × |
21018 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and eighteen |
| Binary (base 2) | 101001000011010 |
| Octal (base 8) | 51032 |
| Hexadecimal (base 16) | 521A |
| Base 3 | 1001211110 |
| As time | 21018 seconds = 5 h 50 min 18 s |
Is 21018 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21018 ÷ 2 = 10509) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21018 ÷ 3 = 7006) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 2) | 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 | Yes (21018 ÷ 6 = 3503) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 2) | 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 8) | 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 6) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21018 a prime number?
No. 21018 = 2 × 3 × 31 × 113, so it is divisible by 2.
What are the factors of 21018?
1, 2, 3, 6, 31, 62, 93, 113, 186, 226, 339, 678, 3503, 7006, 10509, 21018.
What is 21018 in binary?
101001000011010 (hexadecimal 521A, octal 51032).
What is the square root of 21018?
About 144.9759.
Is 21018 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 21018?
21018 is a happy number: repeatedly adding the squares of its digits reaches 1.