21512665666 has 4 divisors (see below), whose sum is σ = 32268998502. Its totient is φ = 10756332832.

The previous prime is 21512665651. The next prime is 21512665679. The reversal of 21512665666 is 66656621512.

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., 14718785041 + 6793880625 = 121321^2 + 82425^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5378166415 + ... + 5378166418.

Almost surely, 2^21512665666 is an apocalyptic number.

21512665666 is a deficient number, since it is larger than the sum of its proper divisors (10756332836).

21512665666 is a wasteful number, since it uses less digits than its factorization.

21512665666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10756332835.

The product of its digits is 777600, while the sum is 46.

The spelling of 21512665666 in words is "twenty-one billion, five hundred twelve million, six hundred sixty-five thousand, six hundred sixty-six".