21566943639 has 12 divisors (see below), whose sum is σ = 31208187816. Its totient is φ = 14352145872.

The previous prime is 21566943613. The next prime is 21566943659. The reversal of 21566943639 is 93634966512.

21566943639 is a `hidden beast` number, since 2 + 1 + 566 + 9 + 43 + 6 + 39 = 666.

It is a de Polignac number, because none of the positive numbers 2^k-21566943639 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21566943659) 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 11 ways as a sum of consecutive naturals, for example, 2146089 + ... + 2156114.

It is an arithmetic number, because the mean of its divisors is an integer number (2600682318).

Almost surely, 2^21566943639 is an apocalyptic number.

21566943639 is a deficient number, since it is larger than the sum of its proper divisors (9641244177).

21566943639 is a wasteful number, since it uses less digits than its factorization.

21566943639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4302766 (or 4302763 counting only the distinct ones).

The product of its digits is 6298560, while the sum is 54.

The spelling of 21566943639 in words is "twenty-one billion, five hundred sixty-six million, nine hundred forty-three thousand, six hundred thirty-nine".