639655864 has 8 divisors (see below), whose sum is σ = 1199354760. Its totient is φ = 319827928.

The previous prime is 639655859. The next prime is 639655867. The reversal of 639655864 is 468556936.

It is a tau number, because it is divible by the number of its divisors (8).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639655867) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39978484 + ... + 39978499.

It is an arithmetic number, because the mean of its divisors is an integer number (149919345).

Almost surely, 2^639655864 is an apocalyptic number.

It is an amenable number.

639655864 is a deficient number, since it is larger than the sum of its proper divisors (559698896).

639655864 is a wasteful number, since it uses less digits than its factorization.

639655864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 79956989 (or 79956985 counting only the distinct ones).

The product of its digits is 4665600, while the sum is 52.

The square root of 639655864 is about 25291.4187818715. The cubic root of 639655864 is about 861.6193861240.

The spelling of 639655864 in words is "six hundred thirty-nine million, six hundred fifty-five thousand, eight hundred sixty-four".