6821 has 4 divisors (see below), whose sum is σ = 7200. Its totient is φ = 6444.

The previous prime is 6803. The next prime is 6823. The reversal of 6821 is 1286.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1286 = 2 ⋅643.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6821 is a prime.

It is a magnanimous number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 6821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 161 + ... + 198.

It is an arithmetic number, because the mean of its divisors is an integer number (1800).

It is an amenable number.

6821 is a deficient number, since it is larger than the sum of its proper divisors (379).

6821 is a wasteful number, since it uses less digits than its factorization.

6821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 378.

The product of its digits is 96, while the sum is 17.

The square root of 6821 is about 82.5893455598. The cubic root of 6821 is about 18.9648472833.

The spelling of 6821 in words is "six thousand, eight hundred twenty-one".