The number 21551
21551 is a composite number with 4 divisors. Its prime factorisation is 23 × 937. Divisors (4): 1, 23, 937, 21551.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21551: a semiprime: 23 × 937, the product of two primes.
- 2
21551 is composite. Its prime factorisation is
- 3
The divisors add up to 22512; without 21551 itself that is 961, so 21551 is deficient (961 is less than 21551). Euler's totient φ(21551) = 20592 numbers up to 21551 share no factor with it.
- 4
The digits of 21551 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21551 = 23 \times 937 \]
21551 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22512 |
| Euler totient φ(n) | 20592 |
| Square | 464445601 |
| Cube | 10009267147151 |
| Square root | 146.802589 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.1551 × |
21551 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand five hundred and fifty-one |
| Binary (base 2) | 101010000101111 |
| Octal (base 8) | 52057 |
| Hexadecimal (base 16) | 542F |
| Base 3 | 1002120012 |
| As time | 21551 seconds = 5 h 59 min 11 s |
Is 21551 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 1) | 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 | No (remainder 5) | 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 5) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 2) | 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 21551 a prime number?
No. 21551 = 23 × 937, so it is divisible by 23.
What are the factors of 21551?
1, 23, 937, 21551.
What is 21551 in binary?
101010000101111 (hexadecimal 542F, octal 52057).
What is the square root of 21551?
About 146.8026.
Is 21551 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21551?
21551 is a semiprime: 23 × 937, the product of two primes.