21108221 has 4 divisors (see below), whose sum is σ = 22219200. Its totient is φ = 19997244.

The previous prime is 21108209. The next prime is 21108233. The reversal of 21108221 is 12280112.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21108209) and next prime (21108233).

It is a cyclic number.

It is not a de Polignac number, because 21108221 - 2²² = 16913917 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21108221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21108251) 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 in 3 ways as a sum of consecutive naturals, for example, 555461 + ... + 555498.

It is an arithmetic number, because the mean of its divisors is an integer number (5554800).

Almost surely, 2^21108221 is an apocalyptic number.

It is an amenable number.

21108221 is a deficient number, since it is larger than the sum of its proper divisors (1110979).

21108221 is a wasteful number, since it uses less digits than its factorization.

21108221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1110978.

The product of its (nonzero) digits is 64, while the sum is 17.

The square root of 21108221 is about 4594.3684005530. The cubic root of 21108221 is about 276.3655320967.

Adding to 21108221 its reverse (12280112), we get a palindrome (33388333).

The spelling of 21108221 in words is "twenty-one million, one hundred eight thousand, two hundred twenty-one".