21105866 has 4 divisors (see below), whose sum is σ = 31658802. Its totient is φ = 10552932.

The previous prime is 21105863. The next prime is 21105907. The reversal of 21105866 is 66850112.

It is a happy number.

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., 15484225 + 5621641 = 3935^2 + 2371^2 .

It is not an unprimeable number, because it can be changed into a prime (21105863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5276465 + ... + 5276468.

Almost surely, 2^21105866 is an apocalyptic number.

21105866 is a deficient number, since it is larger than the sum of its proper divisors (10552936).

21105866 is a wasteful number, since it uses less digits than its factorization.

21105866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10552935.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 21105866 is about 4594.1121013750. The cubic root of 21105866 is about 276.3552538733.

Adding to 21105866 its reverse (66850112), we get a palindrome (87955978).

The spelling of 21105866 in words is "twenty-one million, one hundred five thousand, eight hundred sixty-six".