644939904 has 64 divisors (see below), whose sum is σ = 1957861440. Its totient is φ = 184267776.

The previous prime is 644939899. The next prime is 644939921. The reversal of 644939904 is 409939446.

It is a tau number, because it is divible by the number of its divisors (64).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 117279 + ... + 122654.

It is an arithmetic number, because the mean of its divisors is an integer number (30591585).

Almost surely, 2^644939904 is an apocalyptic number.

644939904 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

644939904 is an abundant number, since it is smaller than the sum of its proper divisors (1312921536).

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

644939904 is a wasteful number, since it uses less digits than its factorization.

644939904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 239957 (or 239945 counting only the distinct ones).

The product of its (nonzero) digits is 839808, while the sum is 48.

The square root of 644939904 is about 25395.6670319958. The cubic root of 644939904 is about 863.9854249942.

The spelling of 644939904 in words is "six hundred forty-four million, nine hundred thirty-nine thousand, nine hundred four".