21664565406 has 24 divisors (see below), whose sum is σ = 51207155064. Its totient is φ = 6565019760.

The previous prime is 21664565401. The next prime is 21664565407. The reversal of 21664565406 is 60456546612.

21664565406 is a `hidden beast` number, since 2 + 1 + 66 + 45 + 6 + 540 + 6 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664565401) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 54708301 + ... + 54708696.

It is an arithmetic number, because the mean of its divisors is an integer number (2133631461).

Almost surely, 2^21664565406 is an apocalyptic number.

21664565406 is an abundant number, since it is smaller than the sum of its proper divisors (29542589658).

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

21664565406 is a wasteful number, since it uses less digits than its factorization.

21664565406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109417016 (or 109417013 counting only the distinct ones).

The product of its (nonzero) digits is 1036800, while the sum is 45.

The spelling of 21664565406 in words is "twenty-one billion, six hundred sixty-four million, five hundred sixty-five thousand, four hundred six".