639808 has 28 divisors (see below), whose sum is σ = 1369060. Its totient is φ = 294912.

The previous prime is 639757. The next prime is 639833. The reversal of 639808 is 808936.

It can be written as a sum of positive squares in 2 ways, for example, as 166464 + 473344 = 408^2 + 688^2 .

It is a congruent number.

It is an unprimeable number.

639808 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 448 + ... + 1216.

It is an arithmetic number, because the mean of its divisors is an integer number (48895).

2⁶³⁹⁸⁰⁸ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (684530).

639808 is an abundant number, since it is smaller than the sum of its proper divisors (729252).

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

639808 is a wasteful number, since it uses less digits than its factorization.

639808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 794 (or 784 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 34.

The square root of 639808 is about 799.8799909986. The cubic root of 639808 is about 86.1687690006.

The spelling of 639808 in words is "six hundred thirty-nine thousand, eight hundred eight".