644020656 has 80 divisors (see below), whose sum is σ = 1854345600. Its totient is φ = 191407104.

The previous prime is 644020651. The next prime is 644020679. The reversal of 644020656 is 656020446.

644020656 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not an unprimeable number, because it can be changed into a prime (644020651) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5266 + ... + 36273.

It is an arithmetic number, because the mean of its divisors is an integer number (23179320).

Almost surely, 2^644020656 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 644020656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (927172800).

644020656 is an abundant number, since it is smaller than the sum of its proper divisors (1210324944).

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

644020656 is a wasteful number, since it uses less digits than its factorization.

644020656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41586 (or 41580 counting only the distinct ones).

The product of its (nonzero) digits is 34560, while the sum is 33.

The square root of 644020656 is about 25377.5620578494. The cubic root of 644020656 is about 863.5747435716.

The spelling of 644020656 in words is "six hundred forty-four million, twenty thousand, six hundred fifty-six".