21123356666 has 16 divisors (see below), whose sum is σ = 33382972800. Its totient is φ = 9996709248.

The previous prime is 21123356651. The next prime is 21123356677. The reversal of 21123356666 is 66665332112.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 210071 + ... + 293898.

It is an arithmetic number, because the mean of its divisors is an integer number (2086435800).

Almost surely, 2^21123356666 is an apocalyptic number.

21123356666 is a deficient number, since it is larger than the sum of its proper divisors (12259616134).

21123356666 is a wasteful number, since it uses less digits than its factorization.

21123356666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 505093.

The product of its digits is 233280, while the sum is 41.

Adding to 21123356666 its reverse (66665332112), we get a palindrome (87788688778).

The spelling of 21123356666 in words is "twenty-one billion, one hundred twenty-three million, three hundred fifty-six thousand, six hundred sixty-six".