639566918 has 4 divisors (see below), whose sum is σ = 959350380. Its totient is φ = 319783458.

The previous prime is 639566897. The next prime is 639566933. The reversal of 639566918 is 819665936.

It is a semiprime because it is the product of two primes.

It is a self number, because there is not a number n which added to its sum of digits gives 639566918.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 159891728 + ... + 159891731.

It is an arithmetic number, because the mean of its divisors is an integer number (239837595).

Almost surely, 2^639566918 is an apocalyptic number.

639566918 is a deficient number, since it is larger than the sum of its proper divisors (319783462).

639566918 is a wasteful number, since it uses less digits than its factorization.

639566918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 319783461.

The product of its digits is 2099520, while the sum is 53.

The square root of 639566918 is about 25289.6602982326. The cubic root of 639566918 is about 861.5794473826.

The spelling of 639566918 in words is "six hundred thirty-nine million, five hundred sixty-six thousand, nine hundred eighteen".