6721999 has 2 divisors, whose sum is σ = 6722000. Its totient is φ = 6721998.

The previous prime is 6721993. The next prime is 6722039. The reversal of 6721999 is 9991276.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 6721999 - 2⁹ = 6721487 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6721993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3360999 + 3361000.

It is an arithmetic number, because the mean of its divisors is an integer number (3361000).

Almost surely, 2^6721999 is an apocalyptic number.

6721999 is a deficient number, since it is larger than the sum of its proper divisors (1).

6721999 is an equidigital number, since it uses as much as digits as its factorization.

6721999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 61236, while the sum is 43.

The square root of 6721999 is about 2592.6818161896. The cubic root of 6721999 is about 188.7264690049.

The spelling of 6721999 in words is "six million, seven hundred twenty-one thousand, nine hundred ninety-nine".