21188218 has 4 divisors (see below), whose sum is σ = 31782330. Its totient is φ = 10594108.

The previous prime is 21188213. The next prime is 21188227. The reversal of 21188218 is 81288112.

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., 11309769 + 9878449 = 3363^2 + 3143^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21188218.

It is not an unprimeable number, because it can be changed into a prime (21188213) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5297053 + ... + 5297056.

Almost surely, 2^21188218 is an apocalyptic number.

21188218 is a deficient number, since it is larger than the sum of its proper divisors (10594112).

21188218 is a wasteful number, since it uses less digits than its factorization.

21188218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10594111.

The product of its digits is 2048, while the sum is 31.

The square root of 21188218 is about 4603.0661520339. The cubic root of 21188218 is about 276.7142199837.

The spelling of 21188218 in words is "twenty-one million, one hundred eighty-eight thousand, two hundred eighteen".