21210312121 has 4 divisors (see below), whose sum is σ = 21216799744. Its totient is φ = 21203824500.

The previous prime is 21210312083. The next prime is 21210312181. The reversal of 21210312121 is 12121301212.

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 21210312121 - 2²⁵ = 21176757689 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21210312095 and 21210312104.

It is not an unprimeable number, because it can be changed into a prime (21210312181) 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, 3238905 + ... + 3245446.

It is an arithmetic number, because the mean of its divisors is an integer number (5304199936).

Almost surely, 2^21210312121 is an apocalyptic number.

It is an amenable number.

21210312121 is a deficient number, since it is larger than the sum of its proper divisors (6487623).

21210312121 is an equidigital number, since it uses as much as digits as its factorization.

21210312121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6487622.

The product of its (nonzero) digits is 48, while the sum is 16.

Adding to 21210312121 its reverse (12121301212), we get a palindrome (33331613333).

The spelling of 21210312121 in words is "twenty-one billion, two hundred ten million, three hundred twelve thousand, one hundred twenty-one".