639906 has 16 divisors (see below), whose sum is σ = 1335744. Its totient is φ = 203984.

The previous prime is 639857. The next prime is 639907. The reversal of 639906 is 609936.

It is a Curzon number.

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 in 7 ways as a sum of consecutive naturals, for example, 2181 + ... + 2456.

It is an arithmetic number, because the mean of its divisors is an integer number (83484).

2⁶³⁹⁹⁰⁶ is an apocalyptic number.

639906 is an abundant number, since it is smaller than the sum of its proper divisors (695838).

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

639906 is a wasteful number, since it uses less digits than its factorization.

639906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4665.

The product of its (nonzero) digits is 8748, while the sum is 33.

The square root of 639906 is about 799.9412478426. The cubic root of 639906 is about 86.1731682934.

The spelling of 639906 in words is "six hundred thirty-nine thousand, nine hundred six".