20211221210021 has 2 divisors, whose sum is σ = 20211221210022. Its totient is φ = 20211221210020.

The previous prime is 20211221209997. The next prime is 20211221210027. The reversal of 20211221210021 is 12001212211202.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19838249620225 + 372971589796 = 4454015^2 + 610714^2 .

It is a cyclic number.

It is not a de Polignac number, because 20211221210021 - 2³⁰ = 20210147468197 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20211221210027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10105610605010 + 10105610605011.

It is an arithmetic number, because the mean of its divisors is an integer number (10105610605011).

Almost surely, 2^{20211221210021} is an apocalyptic number.

It is an amenable number.

20211221210021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20211221210021 is an equidigital number, since it uses as much as digits as its factorization.

20211221210021 is an evil number, because the sum of its binary digits is even.

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

Adding to 20211221210021 its reverse (12001212211202), we get a palindrome (32212433421223).

The spelling of 20211221210021 in words is "twenty trillion, two hundred eleven billion, two hundred twenty-one million, two hundred ten thousand, twenty-one".