639904 has 12 divisors (see below), whose sum is σ = 1259874. Its totient is φ = 319936.

The previous prime is 639857. The next prime is 639907. The reversal of 639904 is 409936.

It can be written as a sum of positive squares in only one way, i.e., 435600 + 204304 = 660^2 + 452^2 .

It is not an unprimeable number, because it can be changed into a prime (639907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9967 + ... + 10030.

2⁶³⁹⁹⁰⁴ is an apocalyptic number.

It is an amenable number.

639904 is a deficient number, since it is larger than the sum of its proper divisors (619970).

639904 is a wasteful number, since it uses less digits than its factorization.

639904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20007 (or 19999 counting only the distinct ones).

The product of its (nonzero) digits is 5832, while the sum is 31.

The square root of 639904 is about 799.9399977498. The cubic root of 639904 is about 86.1730785164.

The spelling of 639904 in words is "six hundred thirty-nine thousand, nine hundred four".