21111121 has 4 divisors (see below), whose sum is σ = 21320244. Its totient is φ = 20902000.

The previous prime is 21111113. The next prime is 21111143. The reversal of 21111121 is 12111112.

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 13068225 + 8042896 = 3615^2 + 2836^2 .

It is a cyclic number.

It is not a de Polignac number, because 21111121 - 2³ = 21111113 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21111098 and 21111107.

It is not an unprimeable number, because it can be changed into a prime (21111191) 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, 104410 + ... + 104611.

It is an arithmetic number, because the mean of its divisors is an integer number (5330061).

Almost surely, 2^21111121 is an apocalyptic number.

It is an amenable number.

21111121 is a deficient number, since it is larger than the sum of its proper divisors (209123).

21111121 is a wasteful number, since it uses less digits than its factorization.

21111121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 209122.

The product of its digits is 4, while the sum is 10.

The square root of 21111121 is about 4594.6839934864. The cubic root of 21111121 is about 276.3781878821.

Adding to 21111121 its reverse (12111112), we get a palindrome (33222233).

Subtracting from 21111121 its reverse (12111112), we obtain a palindrome (9000009).

The spelling of 21111121 in words is "twenty-one million, one hundred eleven thousand, one hundred twenty-one".