21012121021 has 4 divisors (see below), whose sum is σ = 21018455200. Its totient is φ = 21005786844.

The previous prime is 21012121003. The next prime is 21012121043. The reversal of 21012121021 is 12012121012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21012121021 - 2⁷ = 21012120893 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21012120992 and 21012121010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21012121621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3162111 + ... + 3168748.

It is an arithmetic number, because the mean of its divisors is an integer number (5254613800).

Almost surely, 2^21012121021 is an apocalyptic number.

It is an amenable number.

21012121021 is a deficient number, since it is larger than the sum of its proper divisors (6334179).

21012121021 is an equidigital number, since it uses as much as digits as its factorization.

21012121021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6334178.

The product of its (nonzero) digits is 16, while the sum is 13.

Adding to 21012121021 its reverse (12012121012), we get a palindrome (33024242033).

Subtracting from 21012121021 its reverse (12012121012), we obtain a palindrome (9000000009).

The spelling of 21012121021 in words is "twenty-one billion, twelve million, one hundred twenty-one thousand, twenty-one".