644866723 has 4 divisors (see below), whose sum is σ = 647145688. Its totient is φ = 642587760.

The previous prime is 644866699. The next prime is 644866727. The reversal of 644866723 is 327668446.

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

It is a cyclic number.

It is not a de Polignac number, because 644866723 - 2²¹ = 642769571 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644866727) 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 3 ways as a sum of consecutive naturals, for example, 1139058 + ... + 1139623.

It is an arithmetic number, because the mean of its divisors is an integer number (161786422).

Almost surely, 2^644866723 is an apocalyptic number.

644866723 is a deficient number, since it is larger than the sum of its proper divisors (2278965).

644866723 is a wasteful number, since it uses less digits than its factorization.

644866723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2278964.

The product of its digits is 1161216, while the sum is 46.

The square root of 644866723 is about 25394.2261744673. The cubic root of 644866723 is about 863.9527450971.

The spelling of 644866723 in words is "six hundred forty-four million, eight hundred sixty-six thousand, seven hundred twenty-three".