21012121111 has 4 divisors (see below), whose sum is σ = 21014044552. Its totient is φ = 21010197672.

The previous prime is 21012121093. The next prime is 21012121153. The reversal of 21012121111 is 11112121012.

It is a happy number.

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 21012121111 - 2⁵ = 21012121079 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21012121091 and 21012121100.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21012121181) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 945240 + ... + 967213.

It is an arithmetic number, because the mean of its divisors is an integer number (5253511138).

Almost surely, 2^21012121111 is an apocalyptic number.

21012121111 is a deficient number, since it is larger than the sum of its proper divisors (1923441).

21012121111 is a wasteful number, since it uses less digits than its factorization.

21012121111 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1923440.

The product of its (nonzero) digits is 8, while the sum is 13.

Adding to 21012121111 its reverse (11112121012), we get a palindrome (32124242123).

Subtracting from 21012121111 its reverse (11112121012), we obtain a palindrome (9900000099).

It can be divided in two parts, 2101 and 2121111, that added together give a palindrome (2123212).

The spelling of 21012121111 in words is "twenty-one billion, twelve million, one hundred twenty-one thousand, one hundred eleven".