The number 21990
21990 is a composite number with 16 divisors. Its prime factorisation is 2 × 3 × 5 × 733. Divisors (16): 1, 2, 3, 5, 6, 10, 15, 30, 733, 1466, 2199, 3665, 4398, 7330, 10995, 21990.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21990: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21990 is composite. Its prime factorisation is
- 3
The divisors add up to 52848; without 21990 itself that is 30858, so 21990 is abundant (30858 is more than 21990). Euler's totient φ(21990) = 5856 numbers up to 21990 share no factor with it.
- 4
The digits of 21990 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21990 = 2 \times 3 \times 5 \times 733 \]
21990 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 52848 |
| Euler totient φ(n) | 5856 |
| Square | 483560100 |
| Cube | 10633486599000 |
| Square root | 148.290256 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.199 × |
21990 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and ninety |
| Binary (base 2) | 101010111100110 |
| Octal (base 8) | 52746 |
| Hexadecimal (base 16) | 55E6 |
| Base 3 | 1010011110 |
| As time | 21990 seconds = 6 h 6 min 30 s |
Is 21990 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21990 ÷ 2 = 10995) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21990 ÷ 3 = 7330) | 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 (21990 ÷ 5 = 4398) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21990 ÷ 6 = 3665) | 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 6) | 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 (21990 ÷ 10 = 2199) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | 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 21990 a prime number?
No. 21990 = 2 × 3 × 5 × 733, so it is divisible by 2.
What are the factors of 21990?
1, 2, 3, 5, 6, 10, 15, 30, 733, 1466, 2199, 3665, 4398, 7330, 10995, 21990.
What is 21990 in binary?
101010111100110 (hexadecimal 55E6, octal 52746).
What is the square root of 21990?
About 148.2903.
Is 21990 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 21990?
21990 is a happy number: repeatedly adding the squares of its digits reaches 1.