644278668 has 96 divisors (see below), whose sum is σ = 1724889600. Its totient is φ = 185264640.

The previous prime is 644278651. The next prime is 644278709. The reversal of 644278668 is 866872446.

644278668 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a self number, because there is not a number n which added to its sum of digits gives 644278668.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 415158 + ... + 416706.

It is an arithmetic number, because the mean of its divisors is an integer number (17967600).

Almost surely, 2^644278668 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 644278668, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (862444800).

644278668 is an abundant number, since it is smaller than the sum of its proper divisors (1080610932).

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

644278668 is a wasteful number, since it uses less digits than its factorization.

644278668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1727 (or 1725 counting only the distinct ones).

The product of its digits is 3096576, while the sum is 51.

The square root of 644278668 is about 25382.6450158371. The cubic root of 644278668 is about 863.6900519324.

The spelling of 644278668 in words is "six hundred forty-four million, two hundred seventy-eight thousand, six hundred sixty-eight".