644400 has 90 divisors (see below), whose sum is σ = 2248740. Its totient is φ = 170880.

The previous prime is 644383. The next prime is 644401. The reversal of 644400 is 4446.

It is a tau number, because it is divible by the number of its divisors (90).

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

It is a nialpdrome in base 10.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644400.

It is not an unprimeable number, because it can be changed into a prime (644401) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 3511 + ... + 3689.

It is an arithmetic number, because the mean of its divisors is an integer number (24986).

2⁶⁴⁴⁴⁰⁰ is an apocalyptic number.

644400 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1124370).

644400 is an abundant number, since it is smaller than the sum of its proper divisors (1604340).

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

644400 is a wasteful number, since it uses less digits than its factorization.

644400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 203 (or 189 counting only the distinct ones).

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

The square root of 644400 is about 802.7452896156. The cubic root of 644400 is about 86.3744265877.

Adding to 644400 its reverse (4446), we get a palindrome (648846).

The spelling of 644400 in words is "six hundred forty-four thousand, four hundred".