644438016 has 72 divisors (see below), whose sum is σ = 1861308540. Its totient is φ = 214806528.

The previous prime is 644437973. The next prime is 644438021. The reversal of 644438016 is 610834446.

644438016 is a `hidden beast` number, since 644 + 4 + 3 + 8 + 0 + 1 + 6 = 666.

It is a tau number, because it is divible by the number of its divisors (72).

It is a Harshad number since it is a multiple of its sum of digits (36).

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, 951 + ... + 35913.

Almost surely, 2^644438016 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 644438016, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (930654270).

644438016 is an abundant number, since it is smaller than the sum of its proper divisors (1216870524).

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

644438016 is a wasteful number, since it uses less digits than its factorization.

644438016 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34991 (or 34968 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 36.

The square root of 644438016 is about 25385.7837381476. The cubic root of 644438016 is about 863.7612509050.

The spelling of 644438016 in words is "six hundred forty-four million, four hundred thirty-eight thousand, sixteen".