644692864 has 32 divisors (see below), whose sum is σ = 1325787840. Its totient is φ = 311946240.

The previous prime is 644692837. The next prime is 644692889. The reversal of 644692864 is 468296446.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 77269 + ... + 85204.

It is an arithmetic number, because the mean of its divisors is an integer number (41430870).

Almost surely, 2^644692864 is an apocalyptic number.

644692864 is a gapful number since it is divisible by the number (64) formed by its first and last digit.

It is an amenable number.

644692864 is an abundant number, since it is smaller than the sum of its proper divisors (681094976).

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

644692864 is a wasteful number, since it uses less digits than its factorization.

644692864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 162518 (or 162506 counting only the distinct ones).

The product of its digits is 1990656, while the sum is 49.

The square root of 644692864 is about 25390.8027443009. The cubic root of 644692864 is about 863.8750962561.

The spelling of 644692864 in words is "six hundred forty-four million, six hundred ninety-two thousand, eight hundred sixty-four".