644735664 has 120 divisors (see below), whose sum is σ = 1926662400. Its totient is φ = 200672640.

The previous prime is 644735647. The next prime is 644735671. The reversal of 644735664 is 466537446.

It is a happy number.

644735664 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 192597 + ... + 195915.

It is an arithmetic number, because the mean of its divisors is an integer number (16055520).

Almost surely, 2^644735664 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 644735664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (963331200).

644735664 is an abundant number, since it is smaller than the sum of its proper divisors (1281926736).

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

644735664 is a wasteful number, since it uses less digits than its factorization.

644735664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3423 (or 3414 counting only the distinct ones).

The product of its digits is 1451520, while the sum is 45.

The square root of 644735664 is about 25391.6455551821. The cubic root of 644735664 is about 863.8942128711.

The spelling of 644735664 in words is "six hundred forty-four million, seven hundred thirty-five thousand, six hundred sixty-four".