21221222121 has 18 divisors (see below), whose sum is σ = 33692832810. Its totient is φ = 12861346080.

The previous prime is 21221222083. The next prime is 21221222123. The reversal of 21221222121 is 12122212212.

It is a happy number.

21221222121 is a `hidden beast` number, since 212 + 212 + 221 + 21 = 666.

It can be written as a sum of positive squares in only one way, i.e., 17950640400 + 3270581721 = 133980^2 + 57189^2 .

It is not a de Polignac number, because 21221222121 - 2¹¹ = 21221220073 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21221222094 and 21221222103.

It is not an unprimeable number, because it can be changed into a prime (21221222123) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 9742356 + ... + 9744533.

It is an arithmetic number, because the mean of its divisors is an integer number (1871824045).

Almost surely, 2^21221222121 is an apocalyptic number.

It is an amenable number.

21221222121 is a deficient number, since it is larger than the sum of its proper divisors (12471610689).

21221222121 is a wasteful number, since it uses less digits than its factorization.

21221222121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19486917 (or 19486903 counting only the distinct ones).

The product of its digits is 128, while the sum is 18.

Adding to 21221222121 its reverse (12122212212), we get a palindrome (33343434333).

Subtracting from 21221222121 its reverse (12122212212), we obtain a palindrome (9099009909).

It can be divided in two parts, 21221 and 222121, that added together give a palindrome (243342).

The spelling of 21221222121 in words is "twenty-one billion, two hundred twenty-one million, two hundred twenty-two thousand, one hundred twenty-one".