644023 has 4 divisors (see below), whose sum is σ = 672048. Its totient is φ = 616000.

The previous prime is 644009. The next prime is 644029. The reversal of 644023 is 320446.

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 644023 - 2⁵ = 643991 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 (644029) 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 3 ways as a sum of consecutive naturals, for example, 13978 + ... + 14023.

It is an arithmetic number, because the mean of its divisors is an integer number (168012).

2⁶⁴⁴⁰²³ is an apocalyptic number.

644023 is a deficient number, since it is larger than the sum of its proper divisors (28025).

644023 is a wasteful number, since it uses less digits than its factorization.

644023 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28024.

The product of its (nonzero) digits is 576, while the sum is 19.

The square root of 644023 is about 802.5104360692. The cubic root of 644023 is about 86.3575791269.

Adding to 644023 its reverse (320446), we get a palindrome (964469).

The spelling of 644023 in words is "six hundred forty-four thousand, twenty-three".