21002122121 has 4 divisors (see below), whose sum is σ = 21514369044. Its totient is φ = 20489875200.

The previous prime is 21002122109. The next prime is 21002122159. The reversal of 21002122121 is 12122120012.

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 9752550025 + 11249572096 = 98755^2 + 106064^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002122121 - 2¹⁴ = 21002105737 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21002122096 and 21002122105.

It is not an unprimeable number, because it can be changed into a prime (21002122171) 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, 256123400 + ... + 256123481.

It is an arithmetic number, because the mean of its divisors is an integer number (5378592261).

Almost surely, 2^21002122121 is an apocalyptic number.

It is an amenable number.

21002122121 is a deficient number, since it is larger than the sum of its proper divisors (512246923).

21002122121 is an equidigital number, since it uses as much as digits as its factorization.

21002122121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 512246922.

The product of its (nonzero) digits is 32, while the sum is 14.

Adding to 21002122121 its reverse (12122120012), we get a palindrome (33124242133).

The spelling of 21002122121 in words is "twenty-one billion, two million, one hundred twenty-two thousand, one hundred twenty-one".