639405844 has 48 divisors (see below), whose sum is σ = 1399257216. Its totient is φ = 248371200.

The previous prime is 639405821. The next prime is 639405883. The reversal of 639405844 is 448504936.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 639405844.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 105784 + ... + 111664.

It is an arithmetic number, because the mean of its divisors is an integer number (29151192).

Almost surely, 2^639405844 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639405844, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (699628608).

639405844 is an abundant number, since it is smaller than the sum of its proper divisors (759851372).

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

639405844 is a wasteful number, since it uses less digits than its factorization.

639405844 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6256 (or 6254 counting only the distinct ones).

The product of its (nonzero) digits is 414720, while the sum is 43.

The square root of 639405844 is about 25286.4755155795. The cubic root of 639405844 is about 861.5071121319.

The spelling of 639405844 in words is "six hundred thirty-nine million, four hundred five thousand, eight hundred forty-four".