640659 has 4 divisors (see below), whose sum is σ = 854216. Its totient is φ = 427104.

The previous prime is 640649. The next prime is 640663. The reversal of 640659 is 956046.

640659 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 not a de Polignac number, because 640659 - 2⁷ = 640531 is a prime.

It is a D-number.

It is a Duffinian number.

640659 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (640649) 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, 106774 + ... + 106779.

It is an arithmetic number, because the mean of its divisors is an integer number (213554).

2⁶⁴⁰⁶⁵⁹ is an apocalyptic number.

640659 is a deficient number, since it is larger than the sum of its proper divisors (213557).

640659 is a wasteful number, since it uses less digits than its factorization.

640659 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213556.

The product of its (nonzero) digits is 6480, while the sum is 30.

The square root of 640659 is about 800.4117690289. The cubic root of 640659 is about 86.2069560478.

The spelling of 640659 in words is "six hundred forty thousand, six hundred fifty-nine".