21566395844 has 12 divisors (see below), whose sum is σ = 43132791744. Its totient is φ = 9242741064.

The previous prime is 21566395843. The next prime is 21566395861. The reversal of 21566395844 is 44859366512.

It is a happy number.

21566395844 is an admirable number.

It is not an unprimeable number, because it can be changed into a prime (21566395843) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 385114184 + ... + 385114239.

It is an arithmetic number, because the mean of its divisors is an integer number (3594399312).

Almost surely, 2^21566395844 is an apocalyptic number.

It is an amenable number.

21566395844 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21566395844 is a wasteful number, since it uses less digits than its factorization.

21566395844 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 770228434 (or 770228432 counting only the distinct ones).

The product of its digits is 6220800, while the sum is 53.

The spelling of 21566395844 in words is "twenty-one billion, five hundred sixty-six million, three hundred ninety-five thousand, eight hundred forty-four".