644638959 has 16 divisors (see below), whose sum is σ = 969277440. Its totient is φ = 423343800.

The previous prime is 644638949. The next prime is 644638979. The reversal of 644638959 is 959836446.

It is not a de Polignac number, because 644638959 - 2⁵ = 644638927 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644638909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 176367 + ... + 179984.

It is an arithmetic number, because the mean of its divisors is an integer number (60579840).

Almost surely, 2^644638959 is an apocalyptic number.

644638959 is a deficient number, since it is larger than the sum of its proper divisors (324638481).

644638959 is a wasteful number, since it uses less digits than its factorization.

644638959 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 356427 (or 356421 counting only the distinct ones).

The product of its digits is 5598720, while the sum is 54.

The square root of 644638959 is about 25389.7412156958. The cubic root of 644638959 is about 863.8510183901.

The spelling of 644638959 in words is "six hundred forty-four million, six hundred thirty-eight thousand, nine hundred fifty-nine".