644387691 has 4 divisors (see below), whose sum is σ = 859183592. Its totient is φ = 429591792.

The previous prime is 644387687. The next prime is 644387699. The reversal of 644387691 is 196783446.

644387691 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 644387691 - 2² = 644387687 is a prime.

It is a super-2 number, since 2×644387691² = 830470992624622962, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644387691.

It is not an unprimeable number, because it can be changed into a prime (644387699) 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, 107397946 + ... + 107397951.

It is an arithmetic number, because the mean of its divisors is an integer number (214795898).

Almost surely, 2^644387691 is an apocalyptic number.

644387691 is a deficient number, since it is larger than the sum of its proper divisors (214795901).

644387691 is a wasteful number, since it uses less digits than its factorization.

644387691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214795900.

The product of its digits is 870912, while the sum is 48.

The square root of 644387691 is about 25384.7925144170. The cubic root of 644387691 is about 863.7387662411.

The spelling of 644387691 in words is "six hundred forty-four million, three hundred eighty-seven thousand, six hundred ninety-one".