The number 21213
21213 is a composite number with 6 divisors. Its prime factorisation is × 2357. Divisors (6): 1, 3, 9, 2357, 7071, 21213.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21213: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 9.
- 2
21213 is composite. Its prime factorisation is
- 3
The divisors add up to 30654; without 21213 itself that is 9441, so 21213 is deficient (9441 is less than 21213). Euler's totient φ(21213) = 14136 numbers up to 21213 share no factor with it.
- 4
The digits of 21213 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
\[ 21213 = 3^{2} \times 2357 \]21213 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 30654 |
| Euler totient φ(n) | 14136 |
| Square | 449991369 |
| Cube | 9545666910597 |
| Square root | 145.646833 (= 3√2357) |
| Digit sum / digital root | 9 / 9 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1213 × |
21213 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and thirteen |
| Binary (base 2) | 101001011011101 |
| Octal (base 8) | 51335 |
| Hexadecimal (base 16) | 52DD |
| Base 3 | 1002002200 |
| As time | 21213 seconds = 5 h 53 min 33 s |
Is 21213 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 (21213 ÷ 3 = 7071) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | 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 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 3) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21213 ÷ 9 = 2357) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 3) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21213 a prime number?
No. 21213 = × 2357, so it is divisible by 3.
What are the factors of 21213?
1, 3, 9, 2357, 7071, 21213.
What is 21213 in binary?
101001011011101 (hexadecimal 52DD, octal 51335).
What is the square root of 21213?
About 145.6468, exactly 3√2357.
Is 21213 divisible by 3?
Yes. Its digits add up to 9, a multiple of 3.
What is special about the number 21213?
21213 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 9.