21665917836 has 36 divisors (see below), whose sum is σ = 55584044152. Its totient is φ = 7114181184.

The previous prime is 21665917817. The next prime is 21665917837. The reversal of 21665917836 is 63871956612.

21665917836 is a `hidden beast` number, since 2 + 16 + 6 + 591 + 7 + 8 + 36 = 666.

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 (21665917837) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4488865 + ... + 4493688.

Almost surely, 2^21665917836 is an apocalyptic number.

It is an amenable number.

21665917836 is an abundant number, since it is smaller than the sum of its proper divisors (33918126316).

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

21665917836 is a wasteful number, since it uses less digits than its factorization.

21665917836 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8982630 (or 8982625 counting only the distinct ones).

The product of its digits is 3265920, while the sum is 54.

The spelling of 21665917836 in words is "twenty-one billion, six hundred sixty-five million, nine hundred seventeen thousand, eight hundred thirty-six".