644728 has 32 divisors (see below), whose sum is σ = 1432800. Its totient is φ = 266112.

The previous prime is 644717. The next prime is 644729. The reversal of 644728 is 827446.

It is an Ulam number.

It is a self number, because there is not a number n which added to its sum of digits gives 644728.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644729) by changing a digit.

644728 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1426 + ... + 1822.

It is an arithmetic number, because the mean of its divisors is an integer number (44775).

2⁶⁴⁴⁷²⁸ 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 644728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (716400).

644728 is an abundant number, since it is smaller than the sum of its proper divisors (788072).

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

644728 is a wasteful number, since it uses less digits than its factorization.

644728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 439 (or 435 counting only the distinct ones).

The product of its digits is 10752, while the sum is 31.

The square root of 644728 is about 802.9495625505. The cubic root of 644728 is about 86.3890789809.

The spelling of 644728 in words is "six hundred forty-four thousand, seven hundred twenty-eight".