639440 has 20 divisors (see below), whose sum is σ = 1486884. Its totient is φ = 255744.

The previous prime is 639439. The next prime is 639451. The reversal of 639440 is 44936.

It can be written as a sum of positive squares in 2 ways, for example, as 132496 + 506944 = 364^2 + 712^2 .

It is a tau number, because it is divible by the number of its divisors (20).

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 639440.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3917 + ... + 4076.

2⁶³⁹⁴⁴⁰ is an apocalyptic number.

It is an amenable number.

639440 is an abundant number, since it is smaller than the sum of its proper divisors (847444).

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

639440 is a wasteful number, since it uses less digits than its factorization.

639440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8006 (or 8000 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 26.

The square root of 639440 is about 799.6499234040. The cubic root of 639440 is about 86.1522451953.

The spelling of 639440 in words is "six hundred thirty-nine thousand, four hundred forty".