21188866 has 4 divisors (see below), whose sum is σ = 31783302. Its totient is φ = 10594432.

The previous prime is 21188803. The next prime is 21188887. The reversal of 21188866 is 66888112.

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., 19989841 + 1199025 = 4471^2 + 1095^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5297215 + ... + 5297218.

Almost surely, 2^21188866 is an apocalyptic number.

21188866 is a deficient number, since it is larger than the sum of its proper divisors (10594436).

21188866 is a wasteful number, since it uses less digits than its factorization.

21188866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10594435.

The product of its digits is 36864, while the sum is 40.

The square root of 21188866 is about 4603.1365393610. The cubic root of 21188866 is about 276.7170408751.

It can be divided in two parts, 2 and 1188866, that multiplied together give a palindrome (2377732).

The spelling of 21188866 in words is "twenty-one million, one hundred eighty-eight thousand, eight hundred sixty-six".