21002121121 has 4 divisors (see below), whose sum is σ = 21238100100. Its totient is φ = 20766142144.

The previous prime is 21002121073. The next prime is 21002121157. The reversal of 21002121121 is 12112120012.

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 3969000000 + 17033121121 = 63000^2 + 130511^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002121121 - 2⁹ = 21002120609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21002121821) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 117989356 + ... + 117989533.

It is an arithmetic number, because the mean of its divisors is an integer number (5309525025).

Almost surely, 2^21002121121 is an apocalyptic number.

It is an amenable number.

21002121121 is a deficient number, since it is larger than the sum of its proper divisors (235978979).

21002121121 is an equidigital number, since it uses as much as digits as its factorization.

21002121121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 235978978.

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

Adding to 21002121121 its reverse (12112120012), we get a palindrome (33114241133).

The spelling of 21002121121 in words is "twenty-one billion, two million, one hundred twenty-one thousand, one hundred twenty-one".