644000 has 96 divisors (see below), whose sum is σ = 1886976. Its totient is φ = 211200.

The previous prime is 643991. The next prime is 644009. The reversal of 644000 is 446.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (643991) and next prime (644009).

It is a Harshad number since it is a multiple of its sum of digits (14).

It is a nialpdrome in base 10.

It is a congruent number.

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

644000 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, 27989 + ... + 28011.

It is an arithmetic number, because the mean of its divisors is an integer number (19656).

2⁶⁴⁴⁰⁰⁰ 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 644000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (943488).

644000 is an abundant number, since it is smaller than the sum of its proper divisors (1242976).

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

644000 is a wasteful number, since it uses less digits than its factorization.

644000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55 (or 37 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 14.

The square root of 644000 is about 802.4961059096. The cubic root of 644000 is about 86.3565510850.

Adding to 644000 its reverse (446), we get a palindrome (644446).

The spelling of 644000 in words is "six hundred forty-four thousand".