644704685 has 8 divisors (see below), whose sum is σ = 819154296. Its totient is φ = 485424640.

The previous prime is 644704681. The next prime is 644704699. The reversal of 644704685 is 586407446.

It can be written as a sum of positive squares in 4 ways, for example, as 316768804 + 327935881 = 17798^2 + 18109^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 644704685 - 2² = 644704681 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644704681) 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 7 ways as a sum of consecutive naturals, for example, 3792296 + ... + 3792465.

It is an arithmetic number, because the mean of its divisors is an integer number (102394287).

Almost surely, 2^644704685 is an apocalyptic number.

It is an amenable number.

644704685 is a deficient number, since it is larger than the sum of its proper divisors (174449611).

644704685 is a wasteful number, since it uses less digits than its factorization.

644704685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7584783.

The product of its (nonzero) digits is 645120, while the sum is 44.

The square root of 644704685 is about 25391.0355243736. The cubic root of 644704685 is about 863.8803761889.

The spelling of 644704685 in words is "six hundred forty-four million, seven hundred four thousand, six hundred eighty-five".