643897921 has 2 divisors, whose sum is σ = 643897922. Its totient is φ = 643897920.

The previous prime is 643897909. The next prime is 643898027. The reversal of 643897921 is 129798346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 629457921 + 14440000 = 25089^2 + 3800^2 .

It is a cyclic number.

It is not a de Polignac number, because 643897921 - 2⁹ = 643897409 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (643897021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321948960 + 321948961.

It is an arithmetic number, because the mean of its divisors is an integer number (321948961).

Almost surely, 2^643897921 is an apocalyptic number.

It is an amenable number.

643897921 is a deficient number, since it is larger than the sum of its proper divisors (1).

643897921 is an equidigital number, since it uses as much as digits as its factorization.

643897921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 653184, while the sum is 49.

The square root of 643897921 is about 25375.1437631395. The cubic root of 643897921 is about 863.5198811595.

The spelling of 643897921 in words is "six hundred forty-three million, eight hundred ninety-seven thousand, nine hundred twenty-one".