The number 19721
19721 is a composite number with 8 divisors. Its prime factorisation is 13 × 37 × 41. Divisors (8): 1, 13, 37, 41, 481, 533, 1517, 19721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
19721 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
19721 is composite. Its prime factorisation is
- 3
The divisors add up to 22344; without 19721 itself that is 2623, so 19721 is deficient (2623 is less than 19721). Euler's totient φ(19721) = 17280 numbers up to 19721 share no factor with it.
- 4
The digits of 19721 add up to 20, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 61 steps to reach 1.
LaTeX source of the formulas on this page
\[ 19721 = 13 \times 37 \times 41 \]
19721 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 22344 |
| Euler totient φ(n) | 17280 |
| Square | 388917841 |
| Cube | 7669848742361 |
| Square root | 140.431478 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 61 |
| Scientific notation | 1.9721 × |
19721 in other forms
| Form | Value |
|---|---|
| In words | nineteen thousand seven hundred and twenty-one |
| Binary (base 2) | 100110100001001 |
| Octal (base 8) | 46411 |
| Hexadecimal (base 16) | 4D09 |
| Base 3 | 1000001102 |
| As time | 19721 seconds = 5 h 28 min 41 s |
Is 19721 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 1) | 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 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | 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 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 19721 a prime number?
No. 19721 = 13 × 37 × 41, so it is divisible by 13.
What are the factors of 19721?
1, 13, 37, 41, 481, 533, 1517, 19721.
What is 19721 in binary?
100110100001001 (hexadecimal 4D09, octal 46411).
What is the square root of 19721?
About 140.4315.
Is 19721 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 19721?
It is a composite number with 8 divisors.