6399821 has 2 divisors, whose sum is σ = 6399822. Its totient is φ = 6399820.

The previous prime is 6399817. The next prime is 6399829. The reversal of 6399821 is 1289936.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 5929225 + 470596 = 2435^2 + 686^2 .

It is a cyclic number.

It is not a de Polignac number, because 6399821 - 2² = 6399817 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6399829) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3199910 + 3199911.

It is an arithmetic number, because the mean of its divisors is an integer number (3199911).

Almost surely, 2^6399821 is an apocalyptic number.

It is an amenable number.

6399821 is a deficient number, since it is larger than the sum of its proper divisors (1).

6399821 is an equidigital number, since it uses as much as digits as its factorization.

6399821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23328, while the sum is 38.

The square root of 6399821 is about 2529.7867499060. The cubic root of 6399821 is about 185.6618224025.

The spelling of 6399821 in words is "six million, three hundred ninety-nine thousand, eight hundred twenty-one".