639709 has 4 divisors (see below), whose sum is σ = 731104. Its totient is φ = 548316.

The previous prime is 639703. The next prime is 639713. The reversal of 639709 is 907936.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 639709 - 2³ = 639701 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639701) by changing a digit.

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, 45687 + ... + 45700.

It is an arithmetic number, because the mean of its divisors is an integer number (182776).

2⁶³⁹⁷⁰⁹ is an apocalyptic number.

It is an amenable number.

639709 is a deficient number, since it is larger than the sum of its proper divisors (91395).

639709 is an equidigital number, since it uses as much as digits as its factorization.

639709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91394.

The product of its (nonzero) digits is 10206, while the sum is 34.

The square root of 639709 is about 799.8181043212. The cubic root of 639709 is about 86.1643243609.

The spelling of 639709 in words is "six hundred thirty-nine thousand, seven hundred nine".