644784 has 80 divisors (see below), whose sum is σ = 2023680. Its totient is φ = 172800.

The previous prime is 644783. The next prime is 644789. The reversal of 644784 is 487446.

644784 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644783) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6334 + ... + 6434.

It is an arithmetic number, because the mean of its divisors is an integer number (25296).

2⁶⁴⁴⁷⁸⁴ 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 644784, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1011840).

644784 is an abundant number, since it is smaller than the sum of its proper divisors (1378896).

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

644784 is a wasteful number, since it uses less digits than its factorization.

644784 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 138 (or 132 counting only the distinct ones).

The product of its digits is 21504, while the sum is 33.

The square root of 644784 is about 802.9844332240. The cubic root of 644784 is about 86.3915801123.

The spelling of 644784 in words is "six hundred forty-four thousand, seven hundred eighty-four".