644896728 has 112 divisors (see below), whose sum is σ = 2072065680. Its totient is φ = 184244544.

The previous prime is 644896723. The next prime is 644896783. The reversal of 644896728 is 827698446.

644896728 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644896723) by changing a digit.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 32926 + ... + 48722.

Almost surely, 2^644896728 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 644896728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1036032840).

644896728 is an abundant number, since it is smaller than the sum of its proper divisors (1427168952).

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

644896728 is a wasteful number, since it uses less digits than its factorization.

644896728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15828 (or 15809 counting only the distinct ones).

The product of its digits is 4644864, while the sum is 54.

The square root of 644896728 is about 25394.8169514962. The cubic root of 644896728 is about 863.9661445067.

It can be divided in two parts, 64489 and 6728, that added together give a palindrome (71217).

The spelling of 644896728 in words is "six hundred forty-four million, eight hundred ninety-six thousand, seven hundred twenty-eight".