The number 8421
8421 is a composite number with 8 divisors. Its prime factorisation is 3 × 7 × 401. Divisors (8): 1, 3, 7, 21, 401, 1203, 2807, 8421.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
8421 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
8421 is composite. Its prime factorisation is
- 3
The divisors add up to 12864; without 8421 itself that is 4443, so 8421 is deficient (4443 is less than 8421). Euler's totient φ(8421) = 4800 numbers up to 8421 share no factor with it.
- 4
The digits of 8421 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 127 steps to reach 1.
LaTeX source of the formulas on this page
\[ 8421 = 3 \times 7 \times 401 \]
8421 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 12864 |
| Euler totient φ(n) | 4800 |
| Square | 70913241 |
| Cube | 597160402461 |
| Square root | 91.766007 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 127 |
| Scientific notation | 8.421 × |
8421 in other forms
| Form | Value |
|---|---|
| In words | eight thousand four hundred and twenty-one |
| Binary (base 2) | 10000011100101 |
| Octal (base 8) | 20345 |
| Hexadecimal (base 16) | 20E5 |
| Base 3 | 102112220 |
| As time | 8421 seconds = 2 h 20 min 21 s |
Is 8421 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 | Yes (8421 ÷ 3 = 2807) | 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 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (8421 ÷ 7 = 1203) | 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 6) | 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 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 8421 a prime number?
No. 8421 = 3 × 7 × 401, so it is divisible by 3.
What are the factors of 8421?
1, 3, 7, 21, 401, 1203, 2807, 8421.
What is 8421 in binary?
10000011100101 (hexadecimal 20E5, octal 20345).
What is the square root of 8421?
About 91.7660.
Is 8421 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 8421?
It is a composite number with 8 divisors.