664639 has 4 divisors (see below), whose sum is σ = 699640. Its totient is φ = 629640.

The previous prime is 664633. The next prime is 664661. The reversal of 664639 is 936466.

664639 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 664639 - 2⁷ = 664511 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (664633) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17472 + ... + 17509.

It is an arithmetic number, because the mean of its divisors is an integer number (174910).

2⁶⁶⁴⁶³⁹ is an apocalyptic number.

664639 is a deficient number, since it is larger than the sum of its proper divisors (35001).

664639 is a wasteful number, since it uses less digits than its factorization.

664639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35000.

The product of its digits is 23328, while the sum is 34.

The square root of 664639 is about 815.2539481658. The cubic root of 664639 is about 87.2693900305.

The spelling of 664639 in words is "six hundred sixty-four thousand, six hundred thirty-nine".