21212221221 has 32 divisors (see below), whose sum is σ = 31803367680. Its totient is φ = 13971944448.

The previous prime is 21212221193. The next prime is 21212221237. The reversal of 21212221221 is 12212221212.

It is a happy number.

21212221221 is a `hidden beast` number, since 212 + 12 + 221 + 221 = 666.

It is not a de Polignac number, because 21212221221 - 2²³ = 21203832613 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21212221194 and 21212221203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212221321) 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 31 ways as a sum of consecutive naturals, for example, 1609360 + ... + 1622486.

It is an arithmetic number, because the mean of its divisors is an integer number (993855240).

Almost surely, 2^21212221221 is an apocalyptic number.

It is an amenable number.

21212221221 is a deficient number, since it is larger than the sum of its proper divisors (10591146459).

21212221221 is a wasteful number, since it uses less digits than its factorization.

21212221221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13850 (or 13844 counting only the distinct ones).

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

Adding to 21212221221 its reverse (12212221212), we get a palindrome (33424442433).

Subtracting from 21212221221 its reverse (12212221212), we obtain a palindrome (9000000009).

The spelling of 21212221221 in words is "twenty-one billion, two hundred twelve million, two hundred twenty-one thousand, two hundred twenty-one".