21165665508 has 36 divisors (see below), whose sum is σ = 57617646268. Its totient is φ = 6512512320.

The previous prime is 21165665501. The next prime is 21165665513. The reversal of 21165665508 is 80556656112.

21165665508 is a `hidden beast` number, since 21 + 1 + 65 + 6 + 65 + 508 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 4606608384 + 16559057124 = 67872^2 + 128682^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is not an unprimeable number, because it can be changed into a prime (21165665501) 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, 22612423 + ... + 22613358.

Almost surely, 2^21165665508 is an apocalyptic number.

It is an amenable number.

21165665508 is an abundant number, since it is smaller than the sum of its proper divisors (36451980760).

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

21165665508 is a wasteful number, since it uses less digits than its factorization.

21165665508 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45225804 (or 45225799 counting only the distinct ones).

The product of its (nonzero) digits is 432000, while the sum is 45.

The spelling of 21165665508 in words is "twenty-one billion, one hundred sixty-five million, six hundred sixty-five thousand, five hundred eight".