644640726528 has 280 divisors, whose sum is σ = 1967647341528. Its totient is φ = 210819428352.

The previous prime is 644640726523. The next prime is 644640726547. The reversal of 644640726528 is 825627046446.

It is a happy number.

644640726528 is a `hidden beast` number, since 6 + 4 + 4 + 6 + 40 + 72 + 6 + 528 = 666.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644640726523) 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 27 ways as a sum of consecutive naturals, for example, 19765851 + ... + 19798437.

Almost surely, 2^644640726528 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 644640726528, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (983823670764).

644640726528 is an abundant number, since it is smaller than the sum of its proper divisors (1323006615000).

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

644640726528 is an frugal number, since it uses more digits than its factorization.

644640726528 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32676 (or 32645 counting only the distinct ones).

The product of its (nonzero) digits is 15482880, while the sum is 54.

The spelling of 644640726528 in words is "six hundred forty-four billion, six hundred forty million, seven hundred twenty-six thousand, five hundred twenty-eight".