21515866 has 16 divisors (see below), whose sum is σ = 34063200. Its totient is φ = 10164528.

The previous prime is 21515843. The next prime is 21515899. The reversal of 21515866 is 66851512.

It is a happy number.

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 in 7 ways as a sum of consecutive naturals, for example, 25540 + ... + 26368.

It is an arithmetic number, because the mean of its divisors is an integer number (2128950).

Almost surely, 2^21515866 is an apocalyptic number.

21515866 is a deficient number, since it is larger than the sum of its proper divisors (12547334).

21515866 is a wasteful number, since it uses less digits than its factorization.

21515866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1533.

The product of its digits is 14400, while the sum is 34.

The square root of 21515866 is about 4638.5198070074. The cubic root of 21515866 is about 278.1332711591.

The spelling of 21515866 in words is "twenty-one million, five hundred fifteen thousand, eight hundred sixty-six".