644639138 has 32 divisors (see below), whose sum is σ = 1138536000. Its totient is φ = 269876160.

The previous prime is 644639137. The next prime is 644639143. The reversal of 644639138 is 831936446.

It is not an unprimeable number, because it can be changed into a prime (644639137) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 140456 + ... + 144972.

It is an arithmetic number, because the mean of its divisors is an integer number (35579250).

Almost surely, 2^644639138 is an apocalyptic number.

644639138 is a deficient number, since it is larger than the sum of its proper divisors (493896862).

644639138 is a wasteful number, since it uses less digits than its factorization.

644639138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5042.

The product of its digits is 373248, while the sum is 44.

The square root of 644639138 is about 25389.7447407413. The cubic root of 644639138 is about 863.8510983467.

The spelling of 644639138 in words is "six hundred forty-four million, six hundred thirty-nine thousand, one hundred thirty-eight".