644264128 has 56 divisors (see below), whose sum is σ = 1331358272. Its totient is φ = 309049344.

The previous prime is 644264111. The next prime is 644264191. The reversal of 644264128 is 821462446.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 171001 + ... + 174727.

Almost surely, 2^644264128 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 644264128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (665679136).

644264128 is an abundant number, since it is smaller than the sum of its proper divisors (687094144).

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

644264128 is a wasteful number, since it uses less digits than its factorization.

644264128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3849 (or 3839 counting only the distinct ones).

The product of its digits is 73728, while the sum is 37.

The square root of 644264128 is about 25382.3585980499. The cubic root of 644264128 is about 863.6835546674.

The spelling of 644264128 in words is "six hundred forty-four million, two hundred sixty-four thousand, one hundred twenty-eight".