21212111221 has 6 divisors (see below), whose sum is σ = 24675313110. Its totient is φ = 18181809576.

The previous prime is 21212111213. The next prime is 21212111257. The reversal of 21212111221 is 12211121212.

It can be written as a sum of positive squares in only one way, i.e., 15682552900 + 5529558321 = 125230^2 + 74361^2 .

It is not a de Polignac number, because 21212111221 - 2³ = 21212111213 is a prime.

It is a super-2 number, since 2×21212111221² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21212111195 and 21212111204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212111321) 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 5 ways as a sum of consecutive naturals, for example, 216450066 + ... + 216450163.

It is an arithmetic number, because the mean of its divisors is an integer number (4112552185).

Almost surely, 2^21212111221 is an apocalyptic number.

It is an amenable number.

21212111221 is a deficient number, since it is larger than the sum of its proper divisors (3463201889).

21212111221 is an equidigital number, since it uses as much as digits as its factorization.

21212111221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 432900243 (or 432900236 counting only the distinct ones).

The product of its digits is 32, while the sum is 16.

Adding to 21212111221 its reverse (12211121212), we get a palindrome (33423232433).

Subtracting from 21212111221 its reverse (12211121212), we obtain a palindrome (9000990009).

The spelling of 21212111221 in words is "twenty-one billion, two hundred twelve million, one hundred eleven thousand, two hundred twenty-one".