21312312121 has 4 divisors (see below), whose sum is σ = 21355718544. Its totient is φ = 21268905700.

The previous prime is 21312312101. The next prime is 21312312143. The reversal of 21312312121 is 12121321312.

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 a de Polignac number, because none of the positive numbers 2^k-21312312121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21312312101) 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, 21702475 + ... + 21703456.

It is an arithmetic number, because the mean of its divisors is an integer number (5338929636).

Almost surely, 2^21312312121 is an apocalyptic number.

It is an amenable number.

21312312121 is a deficient number, since it is larger than the sum of its proper divisors (43406423).

21312312121 is an equidigital number, since it uses as much as digits as its factorization.

21312312121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43406422.

The product of its digits is 144, while the sum is 19.

Adding to 21312312121 its reverse (12121321312), we get a palindrome (33433633433).

The spelling of 21312312121 in words is "twenty-one billion, three hundred twelve million, three hundred twelve thousand, one hundred twenty-one".