644495621 has 16 divisors (see below), whose sum is σ = 805569408. Its totient is φ = 500928000.

The previous prime is 644495609. The next prime is 644495647. The reversal of 644495621 is 126594446.

It is a cyclic number.

It is not a de Polignac number, because 644495621 - 2⁶ = 644495557 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644495671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 20441 + ... + 41313.

It is an arithmetic number, because the mean of its divisors is an integer number (50348088).

Almost surely, 2^644495621 is an apocalyptic number.

It is an amenable number.

644495621 is a deficient number, since it is larger than the sum of its proper divisors (161073787).

644495621 is a wasteful number, since it uses less digits than its factorization.

644495621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21292.

The product of its digits is 207360, while the sum is 41.

The square root of 644495621 is about 25386.9183045127. The cubic root of 644495621 is about 863.7869867571.

The spelling of 644495621 in words is "six hundred forty-four million, four hundred ninety-five thousand, six hundred twenty-one".