The number 72821
72821 is a composite number with 8 divisors. Its prime factorisation is 7 × 101 × 103. Divisors (8): 1, 7, 101, 103, 707, 721, 10403, 72821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
72821 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
72821 is composite. Its prime factorisation is
- 3
The divisors add up to 84864; without 72821 itself that is 12043, so 72821 is deficient (12043 is less than 72821). Euler's totient φ(72821) = 61200 numbers up to 72821 share no factor with it.
- 4
The digits of 72821 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 187 steps to reach 1.
LaTeX source of the formulas on this page
\[ 72821 = 7 \times 101 \times 103 \]
72821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 84864 |
| Euler totient φ(n) | 61200 |
| Square | 5302898041 |
| Cube | 386162338243661 |
| Square root | 269.853664 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 187 |
| Scientific notation | 7.2821 × |
72821 in other forms
| Form | Value |
|---|---|
| In words | seventy-two thousand eight hundred and twenty-one |
| Binary (base 2) | 10001110001110101 |
| Octal (base 8) | 216165 |
| Hexadecimal (base 16) | 11C75 |
| Base 3 | 10200220002 |
| As time | 72821 seconds = 20 h 13 min 41 s |
Is 72821 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 | Yes (72821 ÷ 7 = 10403) | 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 5) | 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 1) | 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 72821 a prime number?
No. 72821 = 7 × 101 × 103, so it is divisible by 7.
What are the factors of 72821?
1, 7, 101, 103, 707, 721, 10403, 72821.
What is 72821 in binary?
10001110001110101 (hexadecimal 11C75, octal 216165).
What is the square root of 72821?
About 269.8537.
Is 72821 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 72821?
It is a composite number with 8 divisors.