644693639 has 8 divisors (see below), whose sum is σ = 666321408. Its totient is φ = 623117880.

The previous prime is 644693633. The next prime is 644693681. The reversal of 644693639 is 936396446.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 644693639 - 2²⁴ = 627916423 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644693633) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 13064 + ... + 38210.

It is an arithmetic number, because the mean of its divisors is an integer number (83290176).

Almost surely, 2^644693639 is an apocalyptic number.

644693639 is a deficient number, since it is larger than the sum of its proper divisors (21627769).

644693639 is a wasteful number, since it uses less digits than its factorization.

644693639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26005.

The product of its digits is 2519424, while the sum is 50.

The square root of 644693639 is about 25390.8180057280. The cubic root of 644693639 is about 863.8754424172.

The spelling of 644693639 in words is "six hundred forty-four million, six hundred ninety-three thousand, six hundred thirty-nine".