644724 has 18 divisors (see below), whose sum is σ = 1629810. Its totient is φ = 214896.

The previous prime is 644717. The next prime is 644729. The reversal of 644724 is 427446.

It can be written as a sum of positive squares in only one way, i.e., 535824 + 108900 = 732^2 + 330^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8919 + ... + 8990.

It is an arithmetic number, because the mean of its divisors is an integer number (90545).

2⁶⁴⁴⁷²⁴ is an apocalyptic number.

It is an amenable number.

644724 is an abundant number, since it is smaller than the sum of its proper divisors (985086).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644724 is a wasteful number, since it uses less digits than its factorization.

644724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17919 (or 17914 counting only the distinct ones).

The product of its digits is 5376, while the sum is 27.

The square root of 644724 is about 802.9470717301. The cubic root of 644724 is about 86.3889003231.

The spelling of 644724 in words is "six hundred forty-four thousand, seven hundred twenty-four".