21879866 has 4 divisors (see below), whose sum is σ = 32819802. Its totient is φ = 10939932.

The previous prime is 21879841. The next prime is 21879881. The reversal of 21879866 is 66897812.

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., 17347225 + 4532641 = 4165^2 + 2129^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21879866.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5469965 + ... + 5469968.

Almost surely, 2^21879866 is an apocalyptic number.

21879866 is a deficient number, since it is larger than the sum of its proper divisors (10939936).

21879866 is a wasteful number, since it uses less digits than its factorization.

21879866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10939935.

The product of its digits is 290304, while the sum is 47.

The square root of 21879866 is about 4677.5919018230. The cubic root of 21879866 is about 279.6929712796.

The spelling of 21879866 in words is "twenty-one million, eight hundred seventy-nine thousand, eight hundred sixty-six".