644389743440 has 20 divisors (see below), whose sum is σ = 1498206153684. Its totient is φ = 257755897344.

The previous prime is 644389743433. The next prime is 644389743443. The reversal of 644389743440 is 44347983446.

It can be written as a sum of positive squares in 2 ways, for example, as 67968661264 + 576421082176 = 260708^2 + 759224^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644389743443) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4027435817 + ... + 4027435976.

Almost surely, 2^644389743440 is an apocalyptic number.

It is an amenable number.

644389743440 is an abundant number, since it is smaller than the sum of its proper divisors (853816410244).

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

644389743440 is a wasteful number, since it uses less digits than its factorization.

644389743440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8054871806 (or 8054871800 counting only the distinct ones).

The product of its (nonzero) digits is 27869184, while the sum is 56.

The spelling of 644389743440 in words is "six hundred forty-four billion, three hundred eighty-nine million, seven hundred forty-three thousand, four hundred forty".