21212131221 has 24 divisors (see below), whose sum is σ = 32416132320. Its totient is φ = 13329108576.

The previous prime is 21212131153. The next prime is 21212131231. The reversal of 21212131221 is 12213121212.

21212131221 is a `hidden beast` number, since 212 + 121 + 312 + 21 = 666.

It is not a de Polignac number, because 21212131221 - 2⁷ = 21212131093 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21212131194 and 21212131203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212131231) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 281155 + ... + 348528.

It is an arithmetic number, because the mean of its divisors is an integer number (1350672180).

Almost surely, 2^21212131221 is an apocalyptic number.

It is an amenable number.

21212131221 is a deficient number, since it is larger than the sum of its proper divisors (11204001099).

21212131221 is a wasteful number, since it uses less digits than its factorization.

21212131221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 629905 (or 629902 counting only the distinct ones).

The product of its digits is 96, while the sum is 18.

Adding to 21212131221 its reverse (12213121212), we get a palindrome (33425252433).

It can be divided in two parts, 212121 and 31221, that added together give a palindrome (243342).

The spelling of 21212131221 in words is "twenty-one billion, two hundred twelve million, one hundred thirty-one thousand, two hundred twenty-one".