639868 has 12 divisors (see below), whose sum is σ = 1125432. Its totient is φ = 318320.

The previous prime is 639857. The next prime is 639907. The reversal of 639868 is 868936.

It is a self number, because there is not a number n which added to its sum of digits gives 639868.

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 3 ways as a sum of consecutive naturals, for example, 1158 + ... + 1618.

It is an arithmetic number, because the mean of its divisors is an integer number (93786).

2⁶³⁹⁸⁶⁸ is an apocalyptic number.

It is an amenable number.

639868 is a deficient number, since it is larger than the sum of its proper divisors (485564).

639868 is a wasteful number, since it uses less digits than its factorization.

639868 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 812 (or 810 counting only the distinct ones).

The product of its digits is 62208, while the sum is 40.

The square root of 639868 is about 799.9174957457. The cubic root of 639868 is about 86.1714624985.

The spelling of 639868 in words is "six hundred thirty-nine thousand, eight hundred sixty-eight".