644004864 has 88 divisors (see below), whose sum is σ = 1907312720. Its totient is φ = 214659072.

The previous prime is 644004799. The next prime is 644004887. The reversal of 644004864 is 468400446.

644004864 is a `hidden beast` number, since 644 + 0 + 0 + 4 + 8 + 6 + 4 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16002 + ... + 39294.

Almost surely, 2^644004864 is an apocalyptic number.

644004864 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644004864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (953656360).

644004864 is an abundant number, since it is smaller than the sum of its proper divisors (1263307856).

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

644004864 is a wasteful number, since it uses less digits than its factorization.

644004864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23322 (or 23298 counting only the distinct ones).

The product of its (nonzero) digits is 73728, while the sum is 36.

The square root of 644004864 is about 25377.2509149435. The cubic root of 644004864 is about 863.5676849555.

The spelling of 644004864 in words is "six hundred forty-four million, four thousand, eight hundred sixty-four".