644660856 has 240 divisors, whose sum is σ = 2135311200. Its totient is φ = 181149696.

The previous prime is 644660851. The next prime is 644660857. The reversal of 644660856 is 658066446.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644660851) 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 59 ways as a sum of consecutive naturals, for example, 2508280 + ... + 2508536.

It is an arithmetic number, because the mean of its divisors is an integer number (8897130).

Almost surely, 2^644660856 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 644660856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1067655600).

644660856 is an abundant number, since it is smaller than the sum of its proper divisors (1490650344).

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

644660856 is a wasteful number, since it uses less digits than its factorization.

644660856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 368 (or 348 counting only the distinct ones).

The product of its (nonzero) digits is 829440, while the sum is 45.

The square root of 644660856 is about 25390.1724295051. The cubic root of 644660856 is about 863.8607993336.

The spelling of 644660856 in words is "six hundred forty-four million, six hundred sixty thousand, eight hundred fifty-six".