639856 has 40 divisors (see below), whose sum is σ = 1473120. Its totient is φ = 263424.

The previous prime is 639853. The next prime is 639857. The reversal of 639856 is 658936.

639856 = 39² + 40² + ... + 125².

It is a hoax number, since the sum of its digits (37) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639851) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3150 + ... + 3346.

It is an arithmetic number, because the mean of its divisors is an integer number (36828).

2⁶³⁹⁸⁵⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (736560).

639856 is an abundant number, since it is smaller than the sum of its proper divisors (833264).

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

639856 is a wasteful number, since it uses less digits than its factorization.

639856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 241 (or 235 counting only the distinct ones).

The product of its digits is 38880, while the sum is 37.

The square root of 639856 is about 799.9099949369. The cubic root of 639856 is about 86.1709238124.

The spelling of 639856 in words is "six hundred thirty-nine thousand, eight hundred fifty-six".