640979 has 4 divisors (see below), whose sum is σ = 644400. Its totient is φ = 637560.

The previous prime is 640973. The next prime is 640993. The reversal of 640979 is 979046.

It is a happy number.

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 640979 - 2⁴ = 640963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640973) 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, 1412 + ... + 1809.

It is an arithmetic number, because the mean of its divisors is an integer number (161100).

2⁶⁴⁰⁹⁷⁹ is an apocalyptic number.

640979 is a deficient number, since it is larger than the sum of its proper divisors (3421).

640979 is a wasteful number, since it uses less digits than its factorization.

640979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3420.

The product of its (nonzero) digits is 13608, while the sum is 35.

The square root of 640979 is about 800.6116411844. The cubic root of 640979 is about 86.2213067056.

The spelling of 640979 in words is "six hundred forty thousand, nine hundred seventy-nine".