21566943638 has 16 divisors (see below), whose sum is σ = 32509439424. Its totient is φ = 10730592960.

The previous prime is 21566943613. The next prime is 21566943659. The reversal of 21566943638 is 83634966512.

It is a self number, because there is not a number n which added to its sum of digits gives 21566943638.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 306506 + ... + 370242.

It is an arithmetic number, because the mean of its divisors is an integer number (2031839964).

Almost surely, 2^21566943638 is an apocalyptic number.

21566943638 is a deficient number, since it is larger than the sum of its proper divisors (10942495786).

21566943638 is a wasteful number, since it uses less digits than its factorization.

21566943638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64567.

The product of its digits is 5598720, while the sum is 53.

The spelling of 21566943638 in words is "twenty-one billion, five hundred sixty-six million, nine hundred forty-three thousand, six hundred thirty-eight".