21668663657656 has 16 divisors (see below), whose sum is σ = 40642202086200. Its totient is φ = 10830743101344.

The previous prime is 21668663657653. The next prime is 21668663657699. The reversal of 21668663657656 is 65675636686612.

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 polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 448565275 + ... + 448613578.

Almost surely, 2^{21668663657656} is an apocalyptic number.

It is an amenable number.

21668663657656 is a deficient number, since it is larger than the sum of its proper divisors (18973538428544).

21668663657656 is a wasteful number, since it uses less digits than its factorization.

21668663657656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 897181878 (or 897181874 counting only the distinct ones).

The product of its digits is 2351462400, while the sum is 73.

The spelling of 21668663657656 in words is "twenty-one trillion, six hundred sixty-eight billion, six hundred sixty-three million, six hundred fifty-seven thousand, six hundred fifty-six".