21668663657655 has 48 divisors (see below), whose sum is σ = 44084714965824. Its totient is φ = 9637953868800.

The previous prime is 21668663657653. The next prime is 21668663657699. The reversal of 21668663657655 is 55675636686612.

21668663657655 is a `hidden beast` number, since 2 + 16 + 6 + 8 + 6 + 6 + 36 + 576 + 5 + 5 = 666.

21668663657655 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 21668663657655 - 2¹ = 21668663657653 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21668663657653) 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 47 ways as a sum of consecutive naturals, for example, 929574946 + ... + 929598255.

It is an arithmetic number, because the mean of its divisors is an integer number (918431561788).

Almost surely, 2^{21668663657655} is an apocalyptic number.

21668663657655 is an abundant number, since it is smaller than the sum of its proper divisors (22416051308169).

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

21668663657655 is a wasteful number, since it uses less digits than its factorization.

21668663657655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1859173256 (or 1859173253 counting only the distinct ones).

The product of its digits is 1959552000, while the sum is 72.

The spelling of 21668663657655 in words is "twenty-one trillion, six hundred sixty-eight billion, six hundred sixty-three million, six hundred fifty-seven thousand, six hundred fifty-five".