21222121 has 4 divisors (see below), whose sum is σ = 21234132. Its totient is φ = 21210112.

The previous prime is 21222043. The next prime is 21222143. The reversal of 21222121 is 12122212.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 4247721 + 16974400 = 2061^2 + 4120^2 .

It is a cyclic number.

It is not a de Polignac number, because 21222121 - 2²¹ = 19124969 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21222181) 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, 2776 + ... + 7081.

It is an arithmetic number, because the mean of its divisors is an integer number (5308533).

Almost surely, 2^21222121 is an apocalyptic number.

It is an amenable number.

21222121 is a deficient number, since it is larger than the sum of its proper divisors (12011).

21222121 is an equidigital number, since it uses as much as digits as its factorization.

21222121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12010.

The product of its digits is 32, while the sum is 13.

The square root of 21222121 is about 4606.7473340742. The cubic root of 21222121 is about 276.8617303113.

Adding to 21222121 its reverse (12122212), we get a palindrome (33344333).

Subtracting from 21222121 its reverse (12122212), we obtain a palindrome (9099909).

The spelling of 21222121 in words is "twenty-one million, two hundred twenty-two thousand, one hundred twenty-one".