644904 has 72 divisors (see below), whose sum is σ = 1926990. Its totient is φ = 194688.

The previous prime is 644899. The next prime is 644909. The reversal of 644904 is 409446.

644904 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (644899) and next prime (644909).

It can be written as a sum of positive squares in 3 ways, for example, as 396900 + 248004 = 630^2 + 498^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is not an unprimeable number, because it can be changed into a prime (644909) by changing a digit.

644904 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 17 ways as a sum of consecutive naturals, for example, 12142 + ... + 12194.

2⁶⁴⁴⁹⁰⁴ 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 644904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (963495).

644904 is an abundant number, since it is smaller than the sum of its proper divisors (1282086).

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

644904 is a wasteful number, since it uses less digits than its factorization.

644904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91 (or 71 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 644904 is about 803.0591509970. The cubic root of 644904 is about 86.3969391920.

The spelling of 644904 in words is "six hundred forty-four thousand, nine hundred four".