644023138500 has 144 divisors (see below), whose sum is σ = 2321918202240. Its totient is φ = 147205281600.

The previous prime is 644023138489. The next prime is 644023138501. The reversal of 644023138500 is 5831320446.

644023138500 is a `hidden beast` number, since 6 + 4 + 40 + 231 + 385 + 0 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (644023138501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 10191090 + ... + 10254089.

It is an arithmetic number, because the mean of its divisors is an integer number (16124431960).

Almost surely, 2^644023138500 is an apocalyptic number.

644023138500 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644023138500 is an abundant number, since it is smaller than the sum of its proper divisors (1677895063740).

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

644023138500 is a wasteful number, since it uses less digits than its factorization.

644023138500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20445211 (or 20445196 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 36.

Adding to 644023138500 its reverse (5831320446), we get a palindrome (649854458946).

The spelling of 644023138500 in words is "six hundred forty-four billion, twenty-three million, one hundred thirty-eight thousand, five hundred".