21115221 has 4 divisors (see below), whose sum is σ = 28153632. Its totient is φ = 14076812.

The previous prime is 21115189. The next prime is 21115229. The reversal of 21115221 is 12251112.

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 a cyclic number.

It is not a de Polignac number, because 21115221 - 2⁵ = 21115189 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21115221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21115229) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3519201 + ... + 3519206.

It is an arithmetic number, because the mean of its divisors is an integer number (7038408).

Almost surely, 2^21115221 is an apocalyptic number.

It is an amenable number.

21115221 is a deficient number, since it is larger than the sum of its proper divisors (7038411).

21115221 is an equidigital number, since it uses as much as digits as its factorization.

21115221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7038410.

The product of its digits is 40, while the sum is 15.

The square root of 21115221 is about 4595.1301396152. The cubic root of 21115221 is about 276.3960785667.

Adding to 21115221 its reverse (12251112), we get a palindrome (33366333).

The spelling of 21115221 in words is "twenty-one million, one hundred fifteen thousand, two hundred twenty-one".