The number 1621
1621 is a twin prime (1619 and 1621 are both prime) and the 257th prime number. Its only divisors are 1 and 1621.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 1621: a twin prime (1619 and 1621 are both prime); the 257th prime number.
- 2
1621 is prime, so its only factors are 1 and 1621. It is the 257th prime; the next prime is 1627 and the one before is 1619.
- 3
The divisors add up to 1622; without 1621 itself that is 1, so 1621 is deficient (1 is less than 1621). Euler's totient φ(1621) = 1620 numbers up to 1621 share no factor with it.
- 4
The digits of 1621 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 29 steps to reach 1.
1621 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 1622 |
| Euler totient φ(n) | 1620 |
| Square | 2627641 |
| Cube | 4259406061 |
| Square root | 40.261644 |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 29 |
| Scientific notation | 1.621 × |
1621 in other forms
| Form | Value |
|---|---|
| In words | one thousand six hundred and twenty-one |
| Roman numerals | MDCXXI |
| Binary (base 2) | 11001010101 |
| Octal (base 8) | 3125 |
| Hexadecimal (base 16) | 655 |
| Base 3 | 2020001 |
| As time | 1621 seconds = 27 min 1 s |
Is 1621 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 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 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 5) | 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 4) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1621 a prime number?
Yes. 1621 is divisible only by 1 and itself.
What are the factors of 1621?
1, 1621.
What is 1621 in binary?
11001010101 (hexadecimal 655, octal 3125).
What is the square root of 1621?
About 40.2616.
What is 1621 in Roman numerals?
MDCXXI.
Is 1621 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 1621?
1621 is a twin prime (1619 and 1621 are both prime); the 257th prime number.