644538816 has 224 divisors, whose sum is σ = 2063983680. Its totient is φ = 196411392.

The previous prime is 644538793. The next prime is 644538823. The reversal of 644538816 is 618835446.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1086616 + ... + 1087208.

Almost surely, 2^644538816 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 644538816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1031991840).

644538816 is an abundant number, since it is smaller than the sum of its proper divisors (1419444864).

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

644538816 is a wasteful number, since it uses less digits than its factorization.

644538816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 668 (or 652 counting only the distinct ones).

The product of its digits is 552960, while the sum is 45.

The square root of 644538816 is about 25387.7690236854. The cubic root of 644538816 is about 863.8062837309.

The spelling of 644538816 in words is "six hundred forty-four million, five hundred thirty-eight thousand, eight hundred sixteen".