21172111 has 4 divisors (see below), whose sum is σ = 21188824. Its totient is φ = 21155400.

The previous prime is 21172097. The next prime is 21172133. The reversal of 21172111 is 11127112.

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 21172111 - 2²¹ = 19074959 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21172141) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6285 + ... + 9046.

It is an arithmetic number, because the mean of its divisors is an integer number (5297206).

Almost surely, 2^21172111 is an apocalyptic number.

21172111 is a deficient number, since it is larger than the sum of its proper divisors (16713).

21172111 is a wasteful number, since it uses less digits than its factorization.

21172111 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16712.

The product of its digits is 28, while the sum is 16.

The square root of 21172111 is about 4601.3162247340. The cubic root of 21172111 is about 276.6440840586.

Adding to 21172111 its reverse (11127112), we get a palindrome (32299223).

The spelling of 21172111 in words is "twenty-one million, one hundred seventy-two thousand, one hundred eleven".