644534021 has 2 divisors, whose sum is σ = 644534022. Its totient is φ = 644534020.

The previous prime is 644533997. The next prime is 644534027. The reversal of 644534021 is 120435446.

644534021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 379821121 + 264712900 = 19489^2 + 16270^2 .

It is a cyclic number.

It is not a de Polignac number, because 644534021 - 2⁶ = 644533957 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 (644534027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322267010 + 322267011.

It is an arithmetic number, because the mean of its divisors is an integer number (322267011).

Almost surely, 2^644534021 is an apocalyptic number.

It is an amenable number.

644534021 is a deficient number, since it is larger than the sum of its proper divisors (1).

644534021 is an equidigital number, since it uses as much as digits as its factorization.

644534021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 11520, while the sum is 29.

The square root of 644534021 is about 25387.6745882722. The cubic root of 644534021 is about 863.8041416507.

Adding to 644534021 its reverse (120435446), we get a palindrome (764969467).

The spelling of 644534021 in words is "six hundred forty-four million, five hundred thirty-four thousand, twenty-one".