21131111 has 4 divisors (see below), whose sum is σ = 21859800. Its totient is φ = 20402424.

The previous prime is 21131087. The next prime is 21131137. The reversal of 21131111 is 11113112.

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 21131111 - 2¹⁴ = 21114727 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21131092 and 21131101.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21131141) 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, 364301 + ... + 364358.

It is an arithmetic number, because the mean of its divisors is an integer number (5464950).

Almost surely, 2^21131111 is an apocalyptic number.

21131111 is a deficient number, since it is larger than the sum of its proper divisors (728689).

21131111 is an equidigital number, since it uses as much as digits as its factorization.

21131111 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 728688.

The product of its digits is 6, while the sum is 11.

The square root of 21131111 is about 4596.8588188022. The cubic root of 21131111 is about 276.4653940059.

Adding to 21131111 its reverse (11113112), we get a palindrome (32244223).

It can be divided in two parts, 2113111 and 1, that added together give a palindrome (2113112).

The spelling of 21131111 in words is "twenty-one million, one hundred thirty-one thousand, one hundred eleven".