21115664666 has 4 divisors (see below), whose sum is σ = 31673497002. Its totient is φ = 10557832332.

The previous prime is 21115664627. The next prime is 21115664681. The reversal of 21115664666 is 66646651112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20814121441 + 301543225 = 144271^2 + 17365^2 .

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5278916165 + ... + 5278916168.

Almost surely, 2^21115664666 is an apocalyptic number.

21115664666 is a deficient number, since it is larger than the sum of its proper divisors (10557832336).

21115664666 is a wasteful number, since it uses less digits than its factorization.

21115664666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10557832335.

The product of its digits is 311040, while the sum is 44.

The spelling of 21115664666 in words is "twenty-one billion, one hundred fifteen million, six hundred sixty-four thousand, six hundred sixty-six".