639864 has 24 divisors (see below), whose sum is σ = 1733160. Its totient is φ = 213264.

The previous prime is 639857. The next prime is 639907. The reversal of 639864 is 468936.

639864 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a tau number, because it is divible by the number of its divisors (24).

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a d-powerful number, because it can be written as 6 + 3¹² + 8⁵ + 9⁵ + 6³ + 4⁷ .

It is a congruent number.

It is an unprimeable number.

639864 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, 4372 + ... + 4515.

It is an arithmetic number, because the mean of its divisors is an integer number (72215).

2⁶³⁹⁸⁶⁴ is an apocalyptic number.

It is an amenable number.

639864 is an abundant number, since it is smaller than the sum of its proper divisors (1093296).

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

639864 is a wasteful number, since it uses less digits than its factorization.

639864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8899 (or 8892 counting only the distinct ones).

The product of its digits is 31104, while the sum is 36.

The square root of 639864 is about 799.9149954839. The cubic root of 639864 is about 86.1712829372.

The spelling of 639864 in words is "six hundred thirty-nine thousand, eight hundred sixty-four".