644639904 has 192 divisors, whose sum is σ = 2003097600. Its totient is φ = 201118464.

The previous prime is 644639903. The next prime is 644639909. The reversal of 644639904 is 409936446.

It is a happy number.

644639904 is a `hidden beast` number, since 6 + 4 + 4 + 639 + 9 + 0 + 4 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 644639904.

It is not an unprimeable number, because it can be changed into a prime (644639903) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 1756329 + ... + 1756695.

It is an arithmetic number, because the mean of its divisors is an integer number (10432800).

Almost surely, 2^644639904 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 644639904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1001548800).

644639904 is an abundant number, since it is smaller than the sum of its proper divisors (1358457696).

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

644639904 is a wasteful number, since it uses less digits than its factorization.

644639904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 512 (or 498 counting only the distinct ones).

The product of its (nonzero) digits is 559872, while the sum is 45.

The square root of 644639904 is about 25389.7598255675. The cubic root of 644639904 is about 863.8514405070.

The spelling of 644639904 in words is "six hundred forty-four million, six hundred thirty-nine thousand, nine hundred four".