21664591893 has 24 divisors (see below), whose sum is σ = 36917444096. Its totient is φ = 11980418400.

The previous prime is 21664591843. The next prime is 21664591913. The reversal of 21664591893 is 39819546612.

21664591893 is a `hidden beast` number, since 2 + 1 + 6 + 6 + 459 + 189 + 3 = 666.

It is not a de Polignac number, because 21664591893 - 2⁹ = 21664591381 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664591843) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5544538 + ... + 5548443.

Almost surely, 2^21664591893 is an apocalyptic number.

It is an amenable number.

21664591893 is a deficient number, since it is larger than the sum of its proper divisors (15252852203).

21664591893 is a wasteful number, since it uses less digits than its factorization.

21664591893 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11093025 (or 11093022 counting only the distinct ones).

The product of its digits is 2799360, while the sum is 54.

The spelling of 21664591893 in words is "twenty-one billion, six hundred sixty-four million, five hundred ninety-one thousand, eight hundred ninety-three".