The number 2021
2021 is a composite number with 4 divisors. Its prime factorisation is 43 × 47. Divisors (4): 1, 43, 47, 2021.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 2021: a semiprime: 43 × 47, the product of two primes.
- 2
2021 is composite. Its prime factorisation is
- 3
The divisors add up to 2112; without 2021 itself that is 91, so 2021 is deficient (91 is less than 2021). Euler's totient φ(2021) = 1932 numbers up to 2021 share no factor with it.
- 4
The digits of 2021 add up to 5, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 63 steps to reach 1.
LaTeX source of the formulas on this page
\[ 2021 = 43 \times 47 \]
2021 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 2112 |
| Euler totient φ(n) | 1932 |
| Square | 4084441 |
| Cube | 8254655261 |
| Square root | 44.955534 |
| Digit sum / digital root | 5 / 5 |
| Collatz steps to 1 | 63 |
| Scientific notation | 2.021 × |
2021 in other forms
| Form | Value |
|---|---|
| In words | two thousand and twenty-one |
| Roman numerals | MMXXI |
| Binary (base 2) | 11111100101 |
| Octal (base 8) | 3745 |
| Hexadecimal (base 16) | 7E5 |
| Base 3 | 2202212 |
| As time | 2021 seconds = 33 min 41 s |
Is 2021 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 5) | 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 5) | 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 8) | 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 2021 a prime number?
No. 2021 = 43 × 47, so it is divisible by 43.
What are the factors of 2021?
1, 43, 47, 2021.
What is 2021 in binary?
11111100101 (hexadecimal 7E5, octal 3745).
What is the square root of 2021?
About 44.9555.
What is 2021 in Roman numerals?
MMXXI.
Is 2021 divisible by 3?
No. Its digits add up to 5, which is not a multiple of 3.
What is special about the number 2021?
2021 is a semiprime: 43 × 47, the product of two primes.