640404 has 18 divisors (see below), whose sum is σ = 1618890. Its totient is φ = 213456.

The previous prime is 640369. The next prime is 640411. The reversal of 640404 is 404046.

It can be written as a sum of positive squares in only one way, i.e., 636804 + 3600 = 798^2 + 60^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (18).

640404 is a modest number, since divided by 404 gives 64 as remainder.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640404.

It is an unprimeable number.

640404 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8859 + ... + 8930.

2⁶⁴⁰⁴⁰⁴ is an apocalyptic number.

It is an amenable number.

640404 is an abundant number, since it is smaller than the sum of its proper divisors (978486).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

640404 is a wasteful number, since it uses less digits than its factorization.

640404 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17799 (or 17794 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 640404 is about 800.2524601649. The cubic root of 640404 is about 86.1955169457.

The spelling of 640404 in words is "six hundred forty thousand, four hundred four".