644777664851 has 4 divisors (see below), whose sum is σ = 645024803400. Its totient is φ = 644530526304.

The previous prime is 644777664829. The next prime is 644777664877. The reversal of 644777664851 is 158466777446.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644777664851 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644777664821) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 123565361 + ... + 123570578.

It is an arithmetic number, because the mean of its divisors is an integer number (161256200850).

Almost surely, 2^644777664851 is an apocalyptic number.

644777664851 is a deficient number, since it is larger than the sum of its proper divisors (247138549).

644777664851 is a wasteful number, since it uses less digits than its factorization.

644777664851 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247138548.

The product of its digits is 189665280, while the sum is 65.

The spelling of 644777664851 in words is "six hundred forty-four billion, seven hundred seventy-seven million, six hundred sixty-four thousand, eight hundred fifty-one".