991is an odd number,as it is not divisible by 2
The factors for 991 are all the numbers between -991 and 991 , which divide 991 without leaving any remainder. Since 991 divided by -991 is an integer, -991 is a factor of 991 .
Since 991 divided by -991 is a whole number, -991 is a factor of 991
Since 991 divided by -1 is a whole number, -1 is a factor of 991
Multiples of 991 are all integers divisible by 991 , i.e. the remainder of the full division by 991 is zero. There are infinite multiples of 991. The smallest multiples of 991 are:
It is possible to determine using mathematical techniques whether an integer is prime or not.
for 991, the answer is: yes, 991 is a prime number because it only has two different divisors: 1 and itself (991).
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 991). 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 31.48 ). 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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Next prime number: 997