640728 has 48 divisors (see below), whose sum is σ = 1895400. Its totient is φ = 193920.

The previous prime is 640727. The next prime is 640733. The reversal of 640728 is 827046.

640728 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640727) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 388 + ... + 1196.

2⁶⁴⁰⁷²⁸ 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 640728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (947700).

640728 is an abundant number, since it is smaller than the sum of its proper divisors (1254672).

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

640728 is a wasteful number, since it uses less digits than its factorization.

640728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 832 (or 825 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 640728 is about 800.4548706829. The cubic root of 640728 is about 86.2100508124.

The spelling of 640728 in words is "six hundred forty thousand, seven hundred twenty-eight".