639385728 has 32 divisors (see below), whose sum is σ = 1698369360. Its totient is φ = 213128448.

The previous prime is 639385711. The next prime is 639385729. The reversal of 639385728 is 827583936.

It is a tau number, because it is divible by the number of its divisors (32).

It is not an unprimeable number, because it can be changed into a prime (639385729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 832150 + ... + 832917.

Almost surely, 2^639385728 is an apocalyptic number.

It is an amenable number.

639385728 is an abundant number, since it is smaller than the sum of its proper divisors (1058983632).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

639385728 is a wasteful number, since it uses less digits than its factorization.

639385728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1665084 (or 1665072 counting only the distinct ones).

The product of its digits is 2177280, while the sum is 51.

The square root of 639385728 is about 25286.0777504144. The cubic root of 639385728 is about 861.4980775681.

The spelling of 639385728 in words is "six hundred thirty-nine million, three hundred eighty-five thousand, seven hundred twenty-eight".