21212021221 has 2 divisors, whose sum is σ = 21212021222. Its totient is φ = 21212021220.

The previous prime is 21212021161. The next prime is 21212021267. The reversal of 21212021221 is 12212021212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15215222500 + 5996798721 = 123350^2 + 77439^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212021221 - 2¹⁵ = 21211988453 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21212021195 and 21212021204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212021821) 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 as a sum of consecutive naturals, namely, 10606010610 + 10606010611.

It is an arithmetic number, because the mean of its divisors is an integer number (10606010611).

Almost surely, 2^21212021221 is an apocalyptic number.

It is an amenable number.

21212021221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212021221 is an equidigital number, since it uses as much as digits as its factorization.

21212021221 is an odious number, because the sum of its binary digits is odd.

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

Adding to 21212021221 its reverse (12212021212), we get a palindrome (33424042433).

Subtracting from 21212021221 its reverse (12212021212), we obtain a palindrome (9000000009).

The spelling of 21212021221 in words is "twenty-one billion, two hundred twelve million, twenty-one thousand, two hundred twenty-one".