The number 20491
20491 is a composite number with 4 divisors. Its prime factorisation is 31 × 661. Divisors (4): 1, 31, 661, 20491.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 20491: a semiprime: 31 × 661, the product of two primes.
- 2
20491 is composite. Its prime factorisation is
- 3
The divisors add up to 21184; without 20491 itself that is 693, so 20491 is deficient (693 is less than 20491). Euler's totient φ(20491) = 19800 numbers up to 20491 share no factor with it.
- 4
The digits of 20491 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 20491 = 31 \times 661 \]
20491 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 21184 |
| Euler totient φ(n) | 19800 |
| Square | 419881081 |
| Cube | 8603783230771 |
| Square root | 143.146778 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.0491 × |
20491 in other forms
| Form | Value |
|---|---|
| In words | twenty thousand four hundred and ninety-one |
| Binary (base 2) | 101000000001011 |
| Octal (base 8) | 50013 |
| Hexadecimal (base 16) | 500B |
| Base 3 | 1001002221 |
| As time | 20491 seconds = 5 h 41 min 31 s |
Is 20491 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 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 2) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | 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 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 20491 a prime number?
No. 20491 = 31 × 661, so it is divisible by 31.
What are the factors of 20491?
1, 31, 661, 20491.
What is 20491 in binary?
101000000001011 (hexadecimal 500B, octal 50013).
What is the square root of 20491?
About 143.1468.
Is 20491 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 20491?
20491 is a semiprime: 31 × 661, the product of two primes.