644533665 has 48 divisors (see below), whose sum is σ = 1118717568. Its totient is φ = 315775488.

The previous prime is 644533651. The next prime is 644533667. The reversal of 644533665 is 566335446.

It is a happy number.

644533665 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 644533665 - 2⁴ = 644533649 is a prime.

It is not an unprimeable number, because it can be changed into a prime (644533667) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 470812 + ... + 472178.

It is an arithmetic number, because the mean of its divisors is an integer number (23306616).

Almost surely, 2^644533665 is an apocalyptic number.

It is an amenable number.

644533665 is a deficient number, since it is larger than the sum of its proper divisors (474183903).

644533665 is a wasteful number, since it uses less digits than its factorization.

644533665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1478 (or 1435 counting only the distinct ones).

The product of its digits is 777600, while the sum is 42.

The square root of 644533665 is about 25387.6675769949. The cubic root of 644533665 is about 863.8039826137.

The spelling of 644533665 in words is "six hundred forty-four million, five hundred thirty-three thousand, six hundred sixty-five".