644040655 has 16 divisors (see below), whose sum is σ = 799027200. Its totient is φ = 497832480.

The previous prime is 644040629. The next prime is 644040673. The reversal of 644040655 is 556040446.

It is not a de Polignac number, because 644040655 - 2⁹ = 644040143 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644040655.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 108556 + ... + 114334.

It is an arithmetic number, because the mean of its divisors is an integer number (49939200).

Almost surely, 2^644040655 is an apocalyptic number.

644040655 is a deficient number, since it is larger than the sum of its proper divisors (154986545).

644040655 is a wasteful number, since it uses less digits than its factorization.

644040655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6534.

The product of its (nonzero) digits is 57600, while the sum is 34.

The square root of 644040655 is about 25377.9560839718. The cubic root of 644040655 is about 863.5836824426.

The spelling of 644040655 in words is "six hundred forty-four million, forty thousand, six hundred fifty-five".