645728 has 24 divisors (see below), whose sum is σ = 1347192. Its totient is φ = 303616.

The previous prime is 645727. The next prime is 645737. The reversal of 645728 is 827546.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a junction number, because it is equal to n+sod(n) for n = 645694 and 645703.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 50 + ... + 1137.

It is an arithmetic number, because the mean of its divisors is an integer number (56133).

2⁶⁴⁵⁷²⁸ is an apocalyptic number.

645728 is a gapful number since it is divisible by the number (68) formed by its first and last digit.

It is an amenable number.

645728 is an abundant number, since it is smaller than the sum of its proper divisors (701464).

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

645728 is a wasteful number, since it uses less digits than its factorization.

645728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1214 (or 1206 counting only the distinct ones).

The product of its digits is 13440, while the sum is 32.

The square root of 645728 is about 803.5720253966. The cubic root of 645728 is about 86.4337202627.

The spelling of 645728 in words is "six hundred forty-five thousand, seven hundred twenty-eight".