640879 has 4 divisors (see below), whose sum is σ = 647584. Its totient is φ = 634176.

The previous prime is 640873. The next prime is 640891. The reversal of 640879 is 978046.

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 640879 - 2⁵ = 640847 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 (640873) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3207 + ... + 3400.

It is an arithmetic number, because the mean of its divisors is an integer number (161896).

2⁶⁴⁰⁸⁷⁹ is an apocalyptic number.

640879 is a deficient number, since it is larger than the sum of its proper divisors (6705).

640879 is an equidigital number, since it uses as much as digits as its factorization.

640879 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6704.

The product of its (nonzero) digits is 12096, while the sum is 34.

The square root of 640879 is about 800.5491864964. The cubic root of 640879 is about 86.2168226382.

The spelling of 640879 in words is "six hundred forty thousand, eight hundred seventy-nine".