644004 has 48 divisors (see below), whose sum is σ = 1713600. Its totient is φ = 209088.

The previous prime is 643991. The next prime is 644009. The reversal of 644004 is 400446.

644004 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644004.

It is not an unprimeable number, because it can be changed into a prime (644009) by changing a digit.

644004 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7192 + ... + 7280.

It is an arithmetic number, because the mean of its divisors is an integer number (35700).

2⁶⁴⁴⁰⁰⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644004, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (856800).

644004 is an abundant number, since it is smaller than the sum of its proper divisors (1069596).

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

644004 is a wasteful number, since it uses less digits than its factorization.

644004 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 169 (or 161 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 644004 is about 802.4985981296. The cubic root of 644004 is about 86.3567298766.

644004 divided by its sum of digits (18) gives a triangular number (35778 = T₂₆₇).

The spelling of 644004 in words is "six hundred forty-four thousand, four".