644637564 has 18 divisors (see below), whose sum is σ = 1629500600. Its totient is φ = 214879176.

The previous prime is 644637559. The next prime is 644637577. The reversal of 644637564 is 465736446.

It is a happy number.

644637564 is a `hidden beast` number, since 6 + 4 + 4 + 637 + 5 + 6 + 4 = 666.

It is a tau number, because it is divible by the number of its divisors (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8953264 + ... + 8953335.

Almost surely, 2^644637564 is an apocalyptic number.

It is an amenable number.

644637564 is an abundant number, since it is smaller than the sum of its proper divisors (984863036).

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

644637564 is a wasteful number, since it uses less digits than its factorization.

644637564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17906609 (or 17906604 counting only the distinct ones).

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

The square root of 644637564 is about 25389.7137439554. The cubic root of 644637564 is about 863.8503952646.

It can be divided in two parts, 64463 and 7564, that added together give a palindrome (72027).

The spelling of 644637564 in words is "six hundred forty-four million, six hundred thirty-seven thousand, five hundred sixty-four".