821is an odd number,as it is not divisible by 2
The factors for 821 are all the numbers between -821 and 821 , which divide 821 without leaving any remainder. Since 821 divided by -821 is an integer, -821 is a factor of 821 .
Since 821 divided by -821 is a whole number, -821 is a factor of 821
Since 821 divided by -1 is a whole number, -1 is a factor of 821
Multiples of 821 are all integers divisible by 821 , i.e. the remainder of the full division by 821 is zero. There are infinite multiples of 821. The smallest multiples of 821 are:
It is possible to determine using mathematical techniques whether an integer is prime or not.
for 821, the answer is: yes, 821 is a prime number because it only has two different divisors: 1 and itself (821).
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 821). 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 28.653 ). 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.
Previous prime number: 811
Next prime number: 823