644576538666 has 32 divisors (see below), whose sum is σ = 1321065123840. Its totient is φ = 209554806384.

The previous prime is 644576538583. The next prime is 644576538667. The reversal of 644576538666 is 666835675446.

It is a junction number, because it is equal to n+sod(n) for n = 644576538597 and 644576538606.

It is not an unprimeable number, because it can be changed into a prime (644576538667) 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, 1652746 + ... + 2005173.

It is an arithmetic number, because the mean of its divisors is an integer number (41283285120).

Almost surely, 2^644576538666 is an apocalyptic number.

644576538666 is an abundant number, since it is smaller than the sum of its proper divisors (676488585174).

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

644576538666 is a wasteful number, since it uses less digits than its factorization.

644576538666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3658650.

The product of its digits is 522547200, while the sum is 66.

The spelling of 644576538666 in words is "six hundred forty-four billion, five hundred seventy-six million, five hundred thirty-eight thousand, six hundred sixty-six".