644646816 has 96 divisors (see below), whose sum is σ = 2051179200. Its totient is φ = 195344640.

The previous prime is 644646809. The next prime is 644646883. The reversal of 644646816 is 618646446.

It is a tau number, because it is divible by the number of its divisors (96).

It is a nude number because it is divisible by every one of its digits.

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 15 ways as a sum of consecutive naturals, for example, 24411 + ... + 43418.

It is an arithmetic number, because the mean of its divisors is an integer number (21366450).

Almost surely, 2^644646816 is an apocalyptic number.

644646816 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

It is an amenable number.

644646816 is an abundant number, since it is smaller than the sum of its proper divisors (1406532384).

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

644646816 is a wasteful number, since it uses less digits than its factorization.

644646816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67859 (or 67845 counting only the distinct ones).

The product of its digits is 663552, while the sum is 45.

The square root of 644646816 is about 25389.8959430715. The cubic root of 644646816 is about 863.8545279773.

The spelling of 644646816 in words is "six hundred forty-four million, six hundred forty-six thousand, eight hundred sixteen".