6821921 has 2 divisors, whose sum is σ = 6821922. Its totient is φ = 6821920.

The previous prime is 6821911. The next prime is 6821933. The reversal of 6821921 is 1291286.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6431296 + 390625 = 2536^2 + 625^2 .

It is a cyclic number.

It is not a de Polignac number, because 6821921 - 2¹⁰ = 6820897 is a prime.

It is a super-2 number, since 2×6821921² = 93077212260482, which contains 22 as substring.

It is equal to p₄₆₅₂₉₃ and since 6821921 and 465293 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (6821911) 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 as a sum of consecutive naturals, namely, 3410960 + 3410961.

It is an arithmetic number, because the mean of its divisors is an integer number (3410961).

Almost surely, 2^6821921 is an apocalyptic number.

It is an amenable number.

6821921 is a deficient number, since it is larger than the sum of its proper divisors (1).

6821921 is an equidigital number, since it uses as much as digits as its factorization.

6821921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 29.

The square root of 6821921 is about 2611.8807400033. The cubic root of 6821921 is about 189.6570081589.

The spelling of 6821921 in words is "six million, eight hundred twenty-one thousand, nine hundred twenty-one".