The number 21959
21959 is a composite number with 4 divisors. Its prime factorisation is 7 × 3137. Divisors (4): 1, 7, 3137, 21959.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21959: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 7 × 3137, the product of two primes.
- 2
21959 is composite. Its prime factorisation is
- 3
The divisors add up to 25104; without 21959 itself that is 3145, so 21959 is deficient (3145 is less than 21959). Euler's totient φ(21959) = 18816 numbers up to 21959 share no factor with it.
- 4
The digits of 21959 add up to 26, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21959 = 7 \times 3137 \]
21959 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 25104 |
| Euler totient φ(n) | 18816 |
| Square | 482197681 |
| Cube | 10588578877079 |
| Square root | 148.185694 |
| Digit sum / digital root | 26 / 8 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1959 × |
21959 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and fifty-nine |
| Binary (base 2) | 101010111000111 |
| Octal (base 8) | 52707 |
| Hexadecimal (base 16) | 55C7 |
| Base 3 | 1010010022 |
| As time | 21959 seconds = 6 h 5 min 59 s |
Is 21959 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 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 4) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21959 ÷ 7 = 3137) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 8) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 9) | 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 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21959 a prime number?
No. 21959 = 7 × 3137, so it is divisible by 7.
What are the factors of 21959?
1, 7, 3137, 21959.
What is 21959 in binary?
101010111000111 (hexadecimal 55C7, octal 52707).
What is the square root of 21959?
About 148.1857.
Is 21959 divisible by 3?
No. Its digits add up to 26, which is not a multiple of 3.
What is special about the number 21959?
21959 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 7 × 3137, the product of two primes.