641is an odd number,as it is not divisible by 2
The factors for 641 are all the numbers between -641 and 641 , which divide 641 without leaving any remainder. Since 641 divided by -641 is an integer, -641 is a factor of 641 .
Since 641 divided by -641 is a whole number, -641 is a factor of 641
Since 641 divided by -1 is a whole number, -1 is a factor of 641
Since 641 divided by 1 is a whole number, 1 is a factor of 641
Multiples of 641 are all integers divisible by 641 , i.e. the remainder of the full division by 641 is zero. There are infinite multiples of 641. The smallest multiples of 641 are:
0 : in fact, 0 is divisible by any integer, so it is also a multiple of 641 since 0 × 641 = 0
641 : in fact, 641 is a multiple of itself, since 641 is divisible by 641 (it was 641 / 641 = 1, so the rest of this division is zero)
It is possible to determine using mathematical techniques whether an integer is prime or not.
for 641, the answer is: yes, 641 is a prime number because it only has two different divisors: 1 and itself (641).
To know the primality of an integer, we can use several algorithms. The most naive is to try all divisors below the number you want to know if it is prime (in our case 641). We can already eliminate even numbers bigger than 2 (then 4 , 6 , 8 ...). Besides, we can stop at the square root of the number in question (here 25.318 ). Historically, the Eratosthenes screen (which dates back to Antiquity) uses this technique relatively effectively.
More modern techniques include the Atkin screen, probabilistic tests, or the cyclotomic test.
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