The number 649
649 is a composite number with 4 divisors. Its prime factorisation is 11 × 59. Divisors (4): 1, 11, 59, 649.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 649: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 11 × 59, the product of two primes.
- 2
649 is composite. Its prime factorisation is
- 3
The divisors add up to 720; without 649 itself that is 71, so 649 is deficient (71 is less than 649). Euler's totient φ(649) = 580 numbers up to 649 share no factor with it.
- 4
The digits of 649 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 144 steps to reach 1.
LaTeX source of the formulas on this page
\[ 649 = 11 \times 59 \]
649 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 720 |
| Euler totient φ(n) | 580 |
| Square | 421201 |
| Cube | 273359449 |
| Square root | 25.475478 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 144 |
| Scientific notation | 6.49 × |
649 in other forms
| Form | Value |
|---|---|
| In words | six hundred and forty-nine |
| Roman numerals | DCXLIX |
| Binary (base 2) | 1010001001 |
| Octal (base 8) | 1211 |
| Hexadecimal (base 16) | 289 |
| Base 3 | 220001 |
| As time | 649 seconds = 10 min 49 s |
Is 649 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 4) | 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 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 1) | 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 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | Yes (649 ÷ 11 = 59) | 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 649 a prime number?
No. 649 = 11 × 59, so it is divisible by 11.
What are the factors of 649?
1, 11, 59, 649.
What is 649 in binary?
1010001001 (hexadecimal 289, octal 1211).
What is the square root of 649?
About 25.4755.
What is 649 in Roman numerals?
DCXLIX.
Is 649 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 649?
649 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 11 × 59, the product of two primes.