644064013 has 4 divisors (see below), whose sum is σ = 644220540. Its totient is φ = 643907488.

The previous prime is 644064007. The next prime is 644064037. The reversal of 644064013 is 310460446.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 403286724 + 240777289 = 20082^2 + 15517^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644064013 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 (644064053) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71920 + ... + 80377.

It is an arithmetic number, because the mean of its divisors is an integer number (161055135).

Almost surely, 2^644064013 is an apocalyptic number.

It is an amenable number.

644064013 is a deficient number, since it is larger than the sum of its proper divisors (156527).

644064013 is a wasteful number, since it uses less digits than its factorization.

644064013 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 156526.

The product of its (nonzero) digits is 6912, while the sum is 28.

The square root of 644064013 is about 25378.4162823451. The cubic root of 644064013 is about 863.5941224376.

The spelling of 644064013 in words is "six hundred forty-four million, sixty-four thousand, thirteen".