21212012221 has 4 divisors (see below), whose sum is σ = 21212333692. Its totient is φ = 21211690752.

The previous prime is 21212012219. The next prime is 21212012231. The reversal of 21212012221 is 12221021212.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 6579480996 + 14632531225 = 81114^2 + 120965^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212012221 - 2¹ = 21212012219 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21212012195 and 21212012204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212012231) 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, 21630 + ... + 207103.

It is an arithmetic number, because the mean of its divisors is an integer number (5303083423).

Almost surely, 2^21212012221 is an apocalyptic number.

It is an amenable number.

21212012221 is a deficient number, since it is larger than the sum of its proper divisors (321471).

21212012221 is an equidigital number, since it uses as much as digits as its factorization.

21212012221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 321470.

The product of its (nonzero) digits is 64, while the sum is 16.

Adding to 21212012221 its reverse (12221021212), we get a palindrome (33433033433).

The spelling of 21212012221 in words is "twenty-one billion, two hundred twelve million, twelve thousand, two hundred twenty-one".