644333864 has 16 divisors (see below), whose sum is σ = 1279192500. Its totient is φ = 303215872.

The previous prime is 644333863. The next prime is 644333869. The reversal of 644333864 is 468333446.

It can be written as a sum of positive squares in 2 ways, for example, as 614544100 + 29789764 = 24790^2 + 5458^2 .

It is a super-2 number, since 2×644333864² = 830332256594340992, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644333863) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 2368739 + ... + 2369010.

Almost surely, 2^644333864 is an apocalyptic number.

It is an amenable number.

644333864 is a deficient number, since it is larger than the sum of its proper divisors (634858636).

644333864 is a wasteful number, since it uses less digits than its factorization.

644333864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4737772 (or 4737768 counting only the distinct ones).

The product of its digits is 497664, while the sum is 41.

The square root of 644333864 is about 25383.7322708856. The cubic root of 644333864 is about 863.7147156259.

The spelling of 644333864 in words is "six hundred forty-four million, three hundred thirty-three thousand, eight hundred sixty-four".