639840 has 96 divisors (see below), whose sum is σ = 2128896. Its totient is φ = 161280.

The previous prime is 639839. The next prime is 639851. The reversal of 639840 is 48936.

639840 is nontrivially palindromic in base 11.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 639798 and 639807.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14859 + ... + 14901.

It is an arithmetic number, because the mean of its divisors is an integer number (22176).

2⁶³⁹⁸⁴⁰ is an apocalyptic number.

639840 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 639840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1064448).

639840 is an abundant number, since it is smaller than the sum of its proper divisors (1489056).

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

639840 is a wasteful number, since it uses less digits than its factorization.

639840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92 (or 84 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 30.

The square root of 639840 is about 799.8999937492. The cubic root of 639840 is about 86.1702055538.

The spelling of 639840 in words is "six hundred thirty-nine thousand, eight hundred forty".