644000400 has 90 divisors (see below), whose sum is σ = 2234872770. Its totient is φ = 171732480.

The previous prime is 644000389. The next prime is 644000453. The reversal of 644000400 is 4000446.

It can be written as a sum of positive squares in 3 ways, for example, as 4112784 + 639887616 = 2028^2 + 25296^2 .

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 an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 85845 + ... + 93044.

Almost surely, 2^644000400 is an apocalyptic number.

644000400 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644000400 is an abundant number, since it is smaller than the sum of its proper divisors (1590872370).

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

644000400 is a wasteful number, since it uses less digits than its factorization.

644000400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 178913 (or 178899 counting only the distinct ones).

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

The square root of 644000400 is about 25377.1629620019. The cubic root of 644000400 is about 863.5656896419.

Adding to 644000400 its reverse (4000446), we get a palindrome (648000846).

The spelling of 644000400 in words is "six hundred forty-four million, four hundred", and thus it is an aban number.