644918691 has 8 divisors (see below), whose sum is σ = 905149120. Its totient is φ = 407317032.

The previous prime is 644918671. The next prime is 644918693. The reversal of 644918691 is 196819446.

644918691 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 644918691 - 2⁹ = 644918179 is a prime.

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 644918691.

It is not an unprimeable number, because it can be changed into a prime (644918693) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5657125 + ... + 5657238.

It is an arithmetic number, because the mean of its divisors is an integer number (113143640).

Almost surely, 2^644918691 is an apocalyptic number.

644918691 is a deficient number, since it is larger than the sum of its proper divisors (260230429).

644918691 is a wasteful number, since it uses less digits than its factorization.

644918691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11314385.

The product of its digits is 373248, while the sum is 48.

The square root of 644918691 is about 25395.2493785747. The cubic root of 644918691 is about 863.9759523164.

The spelling of 644918691 in words is "six hundred forty-four million, nine hundred eighteen thousand, six hundred ninety-one".