21212121211 has 4 divisors (see below), whose sum is σ = 21212911800. Its totient is φ = 21211330624.

The previous prime is 21212121209. The next prime is 21212121283. The reversal of 21212121211 is 11212121212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21212121211 - 2¹ = 21212121209 is a prime.

It is a super-2 number, since 2×21212121211² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21212161211) 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, 353581 + ... + 409198.

It is an arithmetic number, because the mean of its divisors is an integer number (5303227950).

Almost surely, 2^21212121211 is an apocalyptic number.

21212121211 is a deficient number, since it is larger than the sum of its proper divisors (790589).

21212121211 is an equidigital number, since it uses as much as digits as its factorization.

21212121211 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 790588.

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

Adding to 21212121211 its reverse (11212121212), we get a palindrome (32424242423).

Subtracting from 21212121211 its reverse (11212121212), we obtain a palindrome (9999999999).

It can be divided in two parts, 212121212 and 11, that multiplied together give a palindrome (2333333332).

The spelling of 21212121211 in words is "twenty-one billion, two hundred twelve million, one hundred twenty-one thousand, two hundred eleven".