21121221221 has 2 divisors, whose sum is σ = 21121221222. Its totient is φ = 21121221220.

The previous prime is 21121221193. The next prime is 21121221223. The reversal of 21121221221 is 12212212112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19663050625 + 1458170596 = 140225^2 + 38186^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121221221 - 2⁶ = 21121221157 is a prime.

It is a super-2 number, since 2×21121221221² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

Together with 21121221223, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21121221221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21121221223) 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, 10560610610 + 10560610611.

It is an arithmetic number, because the mean of its divisors is an integer number (10560610611).

Almost surely, 2^21121221221 is an apocalyptic number.

It is an amenable number.

21121221221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121221221 is an equidigital number, since it uses as much as digits as its factorization.

21121221221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64, while the sum is 17.

Adding to 21121221221 its reverse (12212212112), we get a palindrome (33333433333).

The spelling of 21121221221 in words is "twenty-one billion, one hundred twenty-one million, two hundred twenty-one thousand, two hundred twenty-one".