21311212121 has 4 divisors (see below), whose sum is σ = 22564812852. Its totient is φ = 20057611392.

The previous prime is 21311212099. The next prime is 21311212127. The reversal of 21311212121 is 12121211312.

It is a happy number.

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 16081029721 + 5230182400 = 126811^2 + 72320^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311212121 - 2⁶ = 21311212057 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (17), and also a Moran number because the ratio is a prime number: 1253600713 = 21311212121 / (2 + 1 + 3 + 1 + 1 + 2 + 1 + 2 + 1 + 2 + 1).

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 21311212121.

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, 626800340 + ... + 626800373.

It is an arithmetic number, because the mean of its divisors is an integer number (5641203213).

Almost surely, 2^21311212121 is an apocalyptic number.

It is an amenable number.

21311212121 is a deficient number, since it is larger than the sum of its proper divisors (1253600731).

21311212121 is a wasteful number, since it uses less digits than its factorization.

21311212121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1253600730.

The product of its digits is 48, while the sum is 17.

Adding to 21311212121 its reverse (12121211312), we get a palindrome (33432423433).

The spelling of 21311212121 in words is "twenty-one billion, three hundred eleven million, two hundred twelve thousand, one hundred twenty-one".