644347864 has 8 divisors (see below), whose sum is σ = 1208152260. Its totient is φ = 322173928.

The previous prime is 644347861. The next prime is 644347877. The reversal of 644347864 is 468743446.

It is a tau number, because it is divible by the number of its divisors (8).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644347861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40271734 + ... + 40271749.

Almost surely, 2^644347864 is an apocalyptic number.

It is an amenable number.

644347864 is a deficient number, since it is larger than the sum of its proper divisors (563804396).

644347864 is a wasteful number, since it uses less digits than its factorization.

644347864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80543489 (or 80543485 counting only the distinct ones).

The product of its digits is 1548288, while the sum is 46.

The square root of 644347864 is about 25384.0080365572. The cubic root of 644347864 is about 863.7209711399.

The spelling of 644347864 in words is "six hundred forty-four million, three hundred forty-seven thousand, eight hundred sixty-four".