21121111 has 4 divisors (see below), whose sum is σ = 23041224. Its totient is φ = 19201000.

The previous prime is 21121099. The next prime is 21121129. The reversal of 21121111 is 11112112.

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 21121111 - 2¹⁵ = 21088343 is a prime.

It is a super-2 number, since 2×21121111² = 892202659748642, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121171) 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, 960040 + ... + 960061.

It is an arithmetic number, because the mean of its divisors is an integer number (5760306).

Almost surely, 2^21121111 is an apocalyptic number.

21121111 is a deficient number, since it is larger than the sum of its proper divisors (1920113).

21121111 is a wasteful number, since it uses less digits than its factorization.

21121111 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1920112.

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

The square root of 21121111 is about 4595.7709908132. The cubic root of 21121111 is about 276.4217760095.

Adding to 21121111 its reverse (11112112), we get a palindrome (32233223).

It can be divided in two parts, 2112111 and 1, that added together give a palindrome (2112112).

The spelling of 21121111 in words is "twenty-one million, one hundred twenty-one thousand, one hundred eleven".