The number 7721
7721 is a composite number with 4 divisors. Its prime factorisation is 7 × 1103. Divisors (4): 1, 7, 1103, 7721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 7721: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 7 × 1103, the product of two primes.
- 2
7721 is composite. Its prime factorisation is
- 3
The divisors add up to 8832; without 7721 itself that is 1111, so 7721 is deficient (1111 is less than 7721). Euler's totient φ(7721) = 6612 numbers up to 7721 share no factor with it.
- 4
The digits of 7721 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 114 steps to reach 1.
LaTeX source of the formulas on this page
\[ 7721 = 7 \times 1103 \]
7721 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 8832 |
| Euler totient φ(n) | 6612 |
| Square | 59613841 |
| Cube | 460278466361 |
| Square root | 87.869221 |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 114 |
| Scientific notation | 7.721 × |
7721 in other forms
| Form | Value |
|---|---|
| In words | seven thousand seven hundred and twenty-one |
| Binary (base 2) | 1111000101001 |
| Octal (base 8) | 17051 |
| Hexadecimal (base 16) | 1E29 |
| Base 3 | 101120222 |
| As time | 7721 seconds = 2 h 8 min 41 s |
Is 7721 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 (7721 ÷ 7 = 1103) | 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 8) | 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 10) | 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 7721 a prime number?
No. 7721 = 7 × 1103, so it is divisible by 7.
What are the factors of 7721?
1, 7, 1103, 7721.
What is 7721 in binary?
1111000101001 (hexadecimal 1E29, octal 17051).
What is the square root of 7721?
About 87.8692.
Is 7721 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 7721?
7721 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 7 × 1103, the product of two primes.