21311212123 has 4 divisors (see below), whose sum is σ = 21365997120. Its totient is φ = 21256427128.

The previous prime is 21311212099. The next prime is 21311212127. The reversal of 21311212123 is 32121211312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21311212123 - 2²¹ = 21309114971 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21311212123.

It is not an unprimeable number, because it can be changed into a prime (21311212127) 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, 27391915 + ... + 27392692.

It is an arithmetic number, because the mean of its divisors is an integer number (5341499280).

Almost surely, 2^21311212123 is an apocalyptic number.

21311212123 is a deficient number, since it is larger than the sum of its proper divisors (54784997).

21311212123 is an equidigital number, since it uses as much as digits as its factorization.

21311212123 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54784996.

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

Adding to 21311212123 its reverse (32121211312), we get a palindrome (53432423435).

The spelling of 21311212123 in words is "twenty-one billion, three hundred eleven million, two hundred twelve thousand, one hundred twenty-three".