The number 21151
21151 is a composite number with 4 divisors. Its prime factorisation is 13 × 1627. Divisors (4): 1, 13, 1627, 21151.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21151: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 13 × 1627, the product of two primes.
- 2
21151 is composite. Its prime factorisation is
- 3
The divisors add up to 22792; without 21151 itself that is 1641, so 21151 is deficient (1641 is less than 21151). Euler's totient φ(21151) = 19512 numbers up to 21151 share no factor with it.
- 4
The digits of 21151 add up to 10, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 131 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21151 = 13 \times 1627 \]
21151 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22792 |
| Euler totient φ(n) | 19512 |
| Square | 447364801 |
| Cube | 9462212905951 |
| Square root | 145.433834 |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 131 |
| Scientific notation | 2.1151 × |
21151 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and fifty-one |
| Binary (base 2) | 101001010011111 |
| Octal (base 8) | 51237 |
| Hexadecimal (base 16) | 529F |
| Base 3 | 1002000101 |
| As time | 21151 seconds = 5 h 52 min 31 s |
Is 21151 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 4) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | 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 21151 a prime number?
No. 21151 = 13 × 1627, so it is divisible by 13.
What are the factors of 21151?
1, 13, 1627, 21151.
What is 21151 in binary?
101001010011111 (hexadecimal 529F, octal 51237).
What is the square root of 21151?
About 145.4338.
Is 21151 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 21151?
21151 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 13 × 1627, the product of two primes.