The number 21090
21090 is a composite number with 32 divisors. Its prime factorisation is 2 × 3 × 5 × 19 × 37. Divisors (32): 1, 2, 3, 5, 6, 10, 15, 19, 30, 37, 38, 57, 74, 95, 111, 114 … 21090.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21090: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21090 is composite. Its prime factorisation is
- 3
The divisors add up to 54720; without 21090 itself that is 33630, so 21090 is abundant (33630 is more than 21090). Euler's totient φ(21090) = 5184 numbers up to 21090 share no factor with it.
- 4
The digits of 21090 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 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21090 = 2 \times 3 \times 5 \times 19 \times 37 \]
21090 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 32 |
| Sum of divisors | 54720 |
| Euler totient φ(n) | 5184 |
| Square | 444788100 |
| Cube | 9380581029000 |
| Square root | 145.223965 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.109 × |
21090 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and ninety |
| Binary (base 2) | 101001001100010 |
| Octal (base 8) | 51142 |
| Hexadecimal (base 16) | 5262 |
| Base 3 | 1001221010 |
| As time | 21090 seconds = 5 h 51 min 30 s |
Is 21090 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21090 ÷ 2 = 10545) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21090 ÷ 3 = 7030) | 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 | Yes (21090 ÷ 5 = 4218) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21090 ÷ 6 = 3515) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | 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 | Yes (21090 ÷ 10 = 2109) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 3) | 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 21090 a prime number?
No. 21090 = 2 × 3 × 5 × 19 × 37, so it is divisible by 2.
What are the factors of 21090?
1, 2, 3, 5, 6, 10, 15, 19, 30, 37, 38, 57, 74, 95, 111, 114, 185, 190, 222, 285, 370, 555, 570, 703, 1110, 1406, 2109, 3515, 4218, 7030, 10545, 21090.
What is 21090 in binary?
101001001100010 (hexadecimal 5262, octal 51142).
What is the square root of 21090?
About 145.2240.
Is 21090 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 21090?
21090 is a happy number: repeatedly adding the squares of its digits reaches 1.