644748841820 has 48 divisors (see below), whose sum is σ = 1495949249088. Its totient is φ = 232175539200.

The previous prime is 644748841783. The next prime is 644748841829. The reversal of 644748841820 is 28148847446.

It is a Smith number, since the sum of its digits (56) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644748841829) 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, 41216531 + ... + 41232170.

It is an arithmetic number, because the mean of its divisors is an integer number (31165609356).

Almost surely, 2^644748841820 is an apocalyptic number.

It is an amenable number.

644748841820 is an abundant number, since it is smaller than the sum of its proper divisors (851200407268).

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

644748841820 is a wasteful number, since it uses less digits than its factorization.

644748841820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82448750 (or 82448748 counting only the distinct ones).

The product of its (nonzero) digits is 11010048, while the sum is 56.

The spelling of 644748841820 in words is "six hundred forty-four billion, seven hundred forty-eight million, eight hundred forty-one thousand, eight hundred twenty".