Is 821 a prime number?
It is possible to find out using mathematical methods whether a given integer is a prime number or not.
For 821, the answer is: yes, 821 is a prime number because it has only two distinct divisors: 1 and itself (821).
As a consequence, 821 is only a multiple of 1 and 821.
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Since 821 is a prime number, 821 is also a deficient number, that is to say 821 is a natural integer that is strictly larger than the sum of its proper divisors, i.e., the divisors of 821 without 821 itself (that is 1, by definition!).